Washington’s army had no shoes in ‘76. That is EIGHT years before Fr. Serra died in ‘84. Plenty of time to send a donation.
Do you think that these people were unaware of world events? They didn’t live in a vacuum. The clergy, in particular, were well informed with dispatches going back and forth all the time.
Valley Forge was during the winter of 1777-78. How did the donation get to Washington? By ship? Bank transfer? As for hearing about it, no problem, but there is no way that Serra heard, raised the money, got it sent to Washington @ Valley Forge. No way. No Panama Canal no telegraph, nothing. A nice story, no facts.