No, the training droids disappear when they are allocated but before they are spent. (Test it yourself and see that they disappear from interface after you move the slider before you press the green Train button. ) I concede HALF your point I was not paying as much attention to training droids as credits, but I definitely had training droids and way over 3,000 credits earlier.
Ok, it seems now like I have half as much ability with training droids as I do with credits? For Logray I have 25(*), 30(**), 17(***), 14(*****), 3(******) and can allocate1095/7600 to reach Lvl 53/85.