It's likely that ad networks have different install counts from attribution partners. After all, that's the whole point of attribution.
Just make sure you understand how attribution is modeled and done (and agree with that methodology) then use that as the source of truth. You can use what the ad networks report as "installs", but this is mostly just a double check. I've seen some companies be ok with +/- 20% and do really well with UA. Dialing into making ad network installs match your attributed installs just means you're agreeing with a methodology the ad networks like. Obviously if that's what you want go for it, but you should use the attribution model that works best for your business.