No, it's their on air call signs (radio designator). When on side groups, they use their names, but when talking to dispatch, I have heard 1910, 1911, 1913 and 1918 so far.
I remember seeing a list of unit numbers for each area command and also the Id numbers for SGT's LT's and other type units here on the web, but i dont remember what website, i did print it out but damned if i can find it.
Yes those new call numbers are new. I also worked in APD radio and we didnt have as many ID numbers as they do now. When i left they had just started changing the Beat areas. I remember when they split up the NE heights and added foothills area making them the 500's .