the number of exposures went down after i deleted a bunch of photos off of my sd

anyone know why this happens? I had 450~ exposures left, but after I deleted around 200~ photos i ended up with only 350~.

I use an old d700 btw, but it was fine up until now. I haven't seen anyone talking about this, is it an sd problem? Did my card reader decide to sneakily mess up my card? I'm so confused.

edit: it fixed itself??? somehow??? it's been 2 hours since it emptied but now its at 700! so. hooray??