Stens 265-826 is the deck belt replace for the GX20072.
And the Gates number is 6651BR which should be made in the USA
The Stens belts usually come from Mexico
NOW belts do not stretch
They wear thin so sit deeper in the pulleys thus become slack
If a belt goes slack almost instantly then the pulleys are stuffed and in particular the very small drive pulley.
In the old days pulleys were cast iron and these lasted almost indefinately
Modern pulleys are almost universally pressed steel and because of this wear thin & polish so even a JD belt starts to slip almost instantly.
Once belts stat to slip they wear even quicker & are internally damaged so will tend to break with the slightest provocation.
I lost a customer because I pointed out the stack pulley was worn beyond use.
The customer had alreay replaced all of the drive train including the $ 1400 tranny where as all he really needed was a $ 200 pulley.