The thing about identifying glassware is that it often has no definite logo or backstamp.  This makes it difficult to determine whether the glass is a genuine licensed Corelle product or a look-alike.  Perhaps this is of no consequence either, as Corning never made their own sets of glasses anyway.  Even official glassware always has been made by a third-party company, and there is nothing superior about the glass it is made from.  It can be a little deceiving when these items have the Corelle brand name on the box, because it’s too easy to wrongly assume that they are made of break-resistant Corelle glass.  But even official Coordinates glasses are just regular glass and every bit as fragile.

As far as determining which glassware is official, the best option is to study the pattern and compare it to a real piece of Corelle.  If every aspect of the design looks absolutely right, it might be a licensed product.  In any case, if the butterflies look a bit odd, or not all the blossoms are represented, or there aren’t enough dots between the snowflakes, it is probably a look-alike.  There are a lot more look-alikes than there are real ones!

Libbey:

Libbey is worthy of note as one of the makers of glassware to go with early Corelle patterns.  It’s impossible to say if every single one of their products of the 1970s was the real thing or not.  There are examples of Libbey glasses that are licensed Corelle Coordinates, but there are many older glasses with look-alike patterns in diverse styles and designs.  They imitated Snowflake Blue, Butterfly Gold (some in amber glass), Spring Blossom Green (some in green glass) and Old Town Blue.  It appears they made official items in these patterns also, plus Morning Blue.  There is Country Festival and Spice O' Life glassware by Libbey as well.

Libbey Glasses:  This Butterfly Gold version has a coloured rim, and the Spice O' Life version is inscribed with "Bonne Sante".

There are also closed-handle pitchers, beverage jugs and cork-top storage jars that appear to be made early on by Libbey with look-alike designs.  These include Butterfly Gold, Spring Blossom Green, Country Festival and Spice O' Life.  Determining which pitchers are Pyrex and which are made by Libbey is fairly simple.  The Pyrex pitchers will have 'Pyrex' printed on the side as part of the decoration.  They are very thin, lightweight and quite fragile, like laboratory glass.  Libbey pitchers on the other hand, are thicker and more hefty.
 

Genuine Pyrex pitchers have the brand name printed on the side.

As for newer Coordinates patterns, they are too numerous to mention.  Most patterns 1980s and newer include matching glassware, and the majority of these have the distinctive 'single bulge' shape near the base.  Libbey also made beverage jugs in selected patterns for the Corelle Coordinates line. 

Some licensed Libbey glassware is marked with a Crisa logo.  Crisa is a Mexico based subsidiary of Libbey Inc.  Some, but not all of Libbey’s products are marked with an ‘L’ logo.

The typical 'single bulge' shape of many Libbey glasses. 

James Bradley Assoc. (Glassmates):

Products from James Bradley Associates, of Northridge California, are easier to identify.  Almost all of their pieces are marked with copyright ‘1973 James Bradley Assoc Inc’, and some say 1974.  The brand name was Glassmates, but this only appears on the original boxes.  It is highly probable that JBA was only in the business of decorating blank glassware made by other companies.  The patterns they imitated were Butterfly Gold, Snowflake Blue, Spring Blossom Green, Old Town Blue and Spice O' Life.  Their glassware sets were sold in clear glass, as well as with a white finish.

Beverage jugs were also available and they have a similar shape to those made of Pyrex.  The difference is easily spotted though with the large white rectangle front and back of the JBA versions.

Also under the Glassmates brand were pedestal mugs in white opal glass.  They were available in the patterns listed above, plus Blue Heather and Indian Summer.  The mugs themselves were actually made by Federal Glass and some of them have the ‘Shield F’ logo on the bottom.  However most of them have no maker’s mark, but they can be identified by the distinctive 'B' shaped handle.  Please see the menu to the left for more about Pedestal Mugs.

Besides glassware, JBA also put their name on vinyl placemats.  So far only a ‘Butterfly Gold’ version has been noted with a copyright date of 1972.  The pattern is not very convincing and doesn’t actually match the glassware patterns they produced.

 
Indiana Glass:

With the 'Drinkware for Corelle' brand, Indiana Glass appears to have enjoyed a short stint in the 1980s & 90s as an official Corelle glassware supplier.  The shape of their glasses is recognizable by the ‘double bulge’ near the bottom, and so far the following patterns have surfaced in this style:

Apricot Grove
Blue Lily
Country Violets
First Of Spring
Forever Yours
Morning Blue
Symphony

It appears that Indiana Glass also made their own imitation patterns under the ‘Complements’ brand name.  Besides the genuine ones, look-alike versions of Forever Yours and Apricot Grove have been spotted also.  There are other items, like candy dishes, made in this version of Forever Yours.

Unknowns:

There are some styles of glassware of unidentified manufacture which bear authentic looking patterns.  
 

One notable style has been observed in Butterfly Gold, Old Town Blue, Morning Blue, Ribbon Bouquet, Blue Floral and Blue Lily.  It was made in 2 sizes and has a slight hour-glass shape, narrowest in the middle and flared top and bottom; the base is flat and thin.  Another style, which may be related, also has a flat base but the sides are completely straight.  This type has been seen in basically the same variety of patterns as above.

A Woodland Brown pattern has been seen on glassware, and it's possible the design is authentic.  Interestingly, the pattern is printed on a white band near the top of the glass.  Not much else is known, unfortunately.