The solution to this problem would be mandatory sex worker licenses and mandatory yearly counseling that acts as an escape path for trafficking victims.
There are many women police officers in vice and many means with which to tackle sex trafficking, with or without the testimony of specific victims (bearing in mind that sex trafficking almost always involves many victims).
Yearly contact seems ... sparse... there's more sense to be had in mandatory weekly or fortnightly STI checkups, etc. which incorporates contact with trained medical professionals familiar with the ins and outs of te game.