Facebook/messenger blocking?

Okay so I’m just curious but why is that when I look at who I’ve blocked on Facebook it shows every person that I’ve blocked, but when I go to messenger some of those people are not shown ? 

I have my ex blocked on Facebook, and he just has me blocked on messenger, but his name doesn’t show up on the app. I’m assuming it’s because his account is currently deactivated, but the girl he left me for I also blocked her on Facebook (she doesn’t even know I exist at least to my knowledge) her name doesn’t show up on my blocked list on messenger either ? And her account is active. 

I’m just curious if there is like a bug or something on the app or what. I’m just curious as to why this is going on. I know it’s not really that big of deal but any help that would make me understand what’s going on I would greatly appreciate it.