Anyone who speaks with confidence about the value of this set or any other coin ten years in the future will probably be trying to sell you something

Gold proof sets have generally been out of favor and have not participated in the price increases of BU gold pandas that have been spurred by the assembly and sale of BU master sets. The 1994 proof set, however, has seen an increase in value, largely because the BU 1994 G1/2 has become tough to find and expensive, and, apparently, some who assemble master sets have started using the 1994P G1/2 as a substitute. Thus, whatever they are willing to pay for the BU 94 G1/2, they'll apparently pay for the proof 94 G1/2. And to get the 94P G1/2, you usually have to buy a set.

So as to not further hijack the 1994 proof set selling thread of Chris, I'll start a new topic for a few related questions.

The assembly of BU master sets have caused a nice pop in the price of the 1994P proof set, owing to the scarcity of the 94 G1/2 BU. Is there a similar potential for a price increase in the 1990, 1991, & 1993 proof sets due to pressure regarding BU G1/2 for 1990, 1991 & 1993?

I exclude the 1992 proof set, because it is already so expensive that I doubt anyone is going to break up that set to get a BU 92 G1/2 replacement. Similarly, I exclude the 1986-1989 proof sets, because there are relatively more of those proof sets and there appears to be little chance of a near term shortage of BU 1986-1989 G1/2 for master sets.

A few question come to mind:

How accepted is the practice of substituting proof coins for BU? Are all the assemblers of master sets doing it? The coins do have the same panda design, but if you insert a proof coin, it isn't really a BU master set anymore. Or maybe they are just called master sets and anything goes? Or maybe whoever is buying these sets don't care about such numismatic details?

If swapping is widespread, then I assume the price of the BU G1/2 will set the floor for the price of the proof G1/2. And, as the price of the BU G1/2 increases, then the price of the proof set will increase.

I am clearly assuming that the key denomination for the 1990, 1991, & 1993 components of the master set is the G1/2. Perhaps I am wrong for one of the years?

Is one of these three years more likely to be influenced by master set assembly? If so, why?

Disclaimer: I own G1/2 and I own proof sets. But, I'm curious about the questions, so I'll pose them.