Original prices of vintage Heuer

Does anyone have any idea/knowledge of where info on the original prices of vintage pieces might be found? Sold a 1974 Skipper (73463) this summer at auction but need to determine, if possible, the original purchase price. Sales info lost due to multiple moves over 50 years. I know, long shot but the tax man awaiteth. Any help/info very much appreciated

in wich country for what reason you have to pay taxes based on the 50 years increase in value?

anyway:

original price was a few hundred dollar

In the United States. Under Internal Revenue rules, the watch is considered a “collectible” and, if there is value appreciation over its original purchase price, that appreciation is taxed at the rate of 28%. If repairs have been made and paid for, they can be added to the overall cost basis for the watch and can be used to reduce the taxable amount. As for info on the purchase price, I did find a contemporary ad online that didn’t expressly state the Skipper’s price, but did list a Heuer chronograph at $145, reduced from $200. Barring any further info, I’ll probably use that as the basis. Thanks for the response. Very much appreciated.

perhabs here or at another place someone can check, if the tax-praxis, as described, can be possible

i am from germany