I notice that a lot of resurfaced balls (especially storm/roto) have logos partially removed.

I'm concerned that if the logos disappear that the ball would no longer be legal? Or am I overthinking things? 

From the Equipment Spec manual, first paragraph of Bowling Ball Specifications-

Any bowling ball used in USBC certi ed competition must be approved and identi able as a ball listed on the “Approved Ball List” located on the Equipment Speci cations page on www.BOWL. com with the exception of House Balls. Additionally, for identi cation purposes, each ball must have some form of serial number (this may be engraved or re-engraved by the bowler); the ball’s original brand and model names or logos must also be engraved on each ball (these may not be re-engraved by the bowler). No additional logos or designs may be added to a previously approved ball without written consent from the USBC.