how come some unit names have only numbers on it?
There are many different types of units. Battalions are numbered in larger numbers.
It's down to logic really..
It means you are reading something that is refering to a Sensitive unit but because of the classification of the document the Unit can only be referred in Numbers.
e.g. A unit is Secret and its operations is best not known to the regular joe. But that unit have to write something to let the regular joe know that they exist. So in a "Restricted" Level document, they are referred to as HQ 1234.
This usually happens when that unit have to install something within the compounds of another camp, but that unit have to let the RP and Guard personnel know that there will be frequent traffic in and out of that camp from that unit.
So that unit writes to the RP, "HQ 1234 have installed a Gundam Detecting radar in . HQ 1234 will frequently book into the camp to check the condition of this radar. HQ 1234 have notified RSM of and personnel will enter your camp at 1000hrs every wednesday in 12345 MID. Please allow the below personnel from HQ 1234 to proceed"