I don't know exactly what's tested by the health card.
Street girls (paraditas in Spanish) stand in front of their preferred hotel. They often live in there, and are usually given a kickback for bringing guys to the rooms there. because of that they may be reluctant or even refuse to go to other hotels. They have their spot and their hours of operation and are fairly reliable (by sex worker standards). They will rarely do anything without a condom, even BBBJ, for fear of losing their health card, even for more money.
Streetwalkers are girls who don't stand in one spot, generally because they don't want to risk getting caught without a health card. They are much more likely to be drug users. Many are Americans staying in TJ for the cheap drugs and living costs, or Mexicans from the US deported for drug crimes, so often speak good English. They can go to any hotel and are more likely to offer BBBJ or even BBFS, if you are inclined towards risky behavior.