In CA, overages on a junior lien at trustee's sale go to any subsequent jr. lienholders, and if there are none, the overages would go to the owner.

If they pay within 7-days, the tenancy continues.On any subsequent failure to pay, the landlord can serve a "Final Notice to Vacate" the day after rent is due.

Either the HOA will just completely crater.

However, back taxes must be paid either by the tax lien holder or they are sold at subsequent options and you loose your right to redemption, as the junior taxholder can redeem to you and get out of the game. 

I have some tax liens which will have subsequent taxes coming due in May and I am wondering if there is a way to apply surplus (premium, overbid) over what the minimum bid was to the subsequent taxes so they will be paid without me having to put up anymore cash?

We all know that city and state tax revenues are under duress as a result of the lockdowns and subsequent business closures.

This increased knowledge hopefully leads to more profit on subsequent flips.As Thomas stated, RE investing has risk.

We do not see amendments or new filings for their subsequent raises. 

Any subsequent violations and you file for eviction based on the lease violation.

If you can't find a way to value-add for a LOT less than what the subsequently increased value would become, and/or get sufficient enough discounts from MOTIVATED Sellers in the first place, how will your BRRRR plan be possible?