Nobody anywhere can guess the value or condition of a piano without inspecting it on the spot, and checking how well it holds in tune, so your local tuner is the best person to ask.
If your tuner feels that it is safe to remove the action (the working parts of the notes) it may be marked on the back with the action makers' name and number, and I may be able to date this.
You mention "stamps", are these exhibition medals? The piano will have been made after the last event shown, see
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If you find old references or links on this site to pianogen.org, they should refer to pianohistory.info