I know that 6 months is way too soon to be negotiating salaries in any usual context. My context is not usual.
I joined the company as their first employee, after a couple year break from work for grad school. I was offered a lower salary than the one I had when leaving my past job, accepting the whole "we are just starting as a business, so we're starting low". Six months into this job, after my probationary period ended, at my December end-of-year review I got a surprise raise of 10% as a confirmation that they'd like to keep me, and as the company was looking at receiving a major grant soon. That put me roughly at the income level of when I've left my previous job 2.5 years prior.
Now, six further months later, the company has been awarded two major grants and five other people have been employed. While I am not struggling on my salary, I suspect that I am underpaid looking at market rates. Furthermore, I believe that some of the newer employees are paid better than me mostly because of having been in better negotiating position during their recruitment process (higher past salary + our company having had the grant awarded). Those are however only suspicions - I'm not able to point at specific numbers and say "look, I'm underpaid".
Anyway, as my one-year anniversary at the company approaches, I've been considering asking my boss for a one year retrospective meeting, where we'd talk about all the ways I've been able to contribute to the company and the way forward. And recently, in the light of the general feeling of being underpaid, I've started considering including some chat about my compensation in that chat.
Is it weird that I'd have that conversation now, only 6-7 months after I've received my prior raise, or should I wait until my end of year review? Is it going to make me look greedy and ungrateful about the previous raise, or is it understandable given the circumstances?