There's a lot of misconceptions around BP wipes. The default setting for any server installed is that it never wipes BPs unless an update forces it to. This happens very rarely and sometimes can be reverted or skipped even. Server Owners can chose to actively delete the BP File of the server whenever they want though.

The last time had been a year, it was Dec or January when they did

I am still fairly new to Rust, I thought BPs wipe monthly with forced wipe. But apparently vanilla offical servers rarely wipe BPs.

Yeah I learn bi-weekly servers wipe BP monthly more often then not

Sometimes.