I'm not remotely sure they realised how bad things were until quite a way in, because they lacked competent reporting and command structure. I'm also not sure they had many spare troops - or rather I'm sure they do scattered across their vast terrain, but they have duties and aren't free for relocation and training recruits. And besides they'll all be as resolutely useless as the slurry that were chewed up in Ukraine last year.I came across an interesting idea a while ago, suppose that the Russian leadership recognised the problems they had with the quality of their troops early on in the war and took some units off the line for intensive training, while keeping others fighting until they were ready.
I strongly expect that the last few months have been spent trying to train up those newbies from the mobilisation effort. Basic training is about 3-4 months, usually. Surely after a year of fighting, survivors of 2022 should have amassed experience and nous which they can pass on to the new arrivals. Plus they may now have the manpower (and AFV shortage) to not make the same mistake of driving unsupported tanks at everything.