While Thom's response is certainly useful and accurate, I'd like to offer something more 'hands-on' which may be helpful.
Recently the quality of the jhana seems to have changed slightly, very slightly. The main change is that I feel less effort in the jhana.
I'm trying to figure out if this means I have progressd to 2nd jhana or if this is just a different flavour of 1st. On the one hand, I would be surprised to have progressed to 2nd because I hadn't really mastered 1st; it was so shaky. On the other, the descriptions of 2nd jhana seem to be 1st with less effort.
You don't need mastery of all the jhanas, that comes with a shitload of practice but isn't necessary for awakening. What you've described sounds like it could either be a very early version of 2nd, or possibly some sub-jhanic fractal thing; either way, it's at least showing you that you're doing something correctly so it's worth tweaking your technique somewhat.
In 1st jhana, thinking still occurs but the focus of attention is fixed on your object;
pitiand
sukha arise and can then be taken as the focus without trying to change or increase them in any way. This leads them to become stronger and clearer, without any effort on your part, but can get a bit too heavy and annoying after a while. At this point, change the focus and place attention on the mental sense of pleasantness; it's not heavy like the bodily stuff and, if the focus is maintained upon it in the same, natural and effortless way as you did in 1st, it will lead to the stilling of the mind and you'll enter 2nd jhana.
What is it that you're trying to achieve overall in your practice?
Don't stress about mastery, like I said, it'll happen if you practice well enough. Familiarize yourself with as much of the jhanic strata as you have access to, even if it's just a hint of what's possible it'll encourage you and keep your practice strong. Even if it's just devoting 5 or 10 minutes of your sit to playing around with concentration and attention, have fun with it and don't let yourself get too hung up on goals and attainments.
Enjoy.