Inverted Year Slug In Duplex?

Good afternoon! OK, I have a question for you. I have an offer to buy this for a few bucks ($10.00 shipped) and I noticed it has the year 1919 as 6161.... What do you think? There was no mention of it in the description so would it be too much to spend around $10.00 on this you think? Thanks for any advice. -Jeff

Personally, I wouldn't spend that much for the cover. The inverted "1919" date isn't going to give much (if any) added value to the cover, in my opinion.

For whatever it's worth, the cover is dated one month to the day after the birth of the addressee's daughter, therefore it is quite probable that the "special delivery" mailing was a congratulatory letter of some sort from a friend or family member:

Thank you. I think I'll heed your advice but the history is really neat though. :)