When I first got into running OP I had basically that exact trajectory. 2 months after I ran 1:30 I ran 3:11, after being on 3:05 (BQ for me at the time) pace through 20 miles. Those were spring races. I ran shorter stuff over the summer then ~5 months after the 1:30 I ran 1:26. Then I ran my BQ (3:03) 1 month later (6 months post 1:30). Then there was some rapid improvement. I ran 1:20 a month after the 3:03 & then 2:53 (w./ bad pacing going for sub-2:50) another month later. So that's all within 8 months of the 1:30-flat. I was young, new to running/undertrained, and just started to grind out higher mileage without really knowing what I was doing. & clearly racing too much/probably not recovering.
Seems reasonable to get pretty close to sub-3 with a bump to something like 60-70mpw.