t Peirce says "every true Proposition" -- a phrase
&gt; which is consistent with the assumption that there exist
&gt; more than one true proposition, even infinitely many.

Yes, but here he is using the word "proposition" in a way
that we no longer do, to mean the actual sign or sentence.
Anyway, that is the way that I have to interpret his usage,
considering this standard portion of his sign classification:

| Sign
|    Index
|    Icon
|    Symbol
|       Term
|       Proposition
|       Argument
|        