Tubing decals on frames can represent a number of things, and not necessarily what tubes were used in the construction of said frame. Tubing decals were certainly, as Jim Merz mentions, marketing tools. Marketing tools not only for tubing manufacturers but for small frame builders and large manufacturers alike. Not all, of course, but I would suspect that "most" would apply.
For a period of time that I'll call the "mid-to-late" time frame of what we consider on-topic here, there certainly was the perception in the marketplace that use of one of the premier tubing sets (mostly Reynolds and Columbus) not only denoted quality, but also positioned the frame in the upper tier of competing products. Most consumers didn't think too far past the decal. I think builders and manufacturers understood this, particularly in the UK. The Stan Pike frame I have is a great example. It was built in 1983 and sports Reynolds 531SL decals on the frame and fork legs. Since I have copies of the original build sheet and notes from Stan's log book, I have much more information about the frame than probably the first two owners (I'm the third). From the log book we learn that this particular frame was not a custom build for a customer, but rather a frame for "stock". From the details in the frame and finish it has been speculated that the frame was likely a "show" frame. Most telling is the information in the build sheet, which specifically identifies the tubing used. Pike built this frame with Reynolds top, seat and head tubes; Columbus fork blades; and Super Vitus down tube, chain and seat stays.
It would seem that Mr. Pike chose the tubes used based on his perception of best performance/applicability for this particular frame. I suppose that some might say he may have just used what he had on hand, but from what I've learned about Stan and his frames, I don't think this is the case. Still, he chose to put Reynolds decals on the frame and fork. Was this just marketing? Did he have some "arrangement" with Reynolds?
Another interesting detail with this frame is the use of a "Silver Brazed" decal on the seat tube, and even "SILVER BRAZED" stamped into the BB shell. Marketing? Possibly, but that's another discussion.
Wayne
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Wayne Bingham
Velo Classique
PO Box 2069
Purcellville, VA 20134 USA
540-338-8376
http://www.veloclassique.com