I dont have a 1.5 year "rest" sample, but I have noticed that in Dec/Jan timeframe, which is "base" my HR is like a hummingbird. I'll do what feels like a threshold effort and HR will be around 180 - 185 bpm. Whereas, this time of year when I'm in peak race form, my HR is lower except for end of race sprints (sprints will hit high 180s, low 190s), and threshold efforts stabilize around mid 170s.
I attribute it to a combo of being more rested in the base training months (HR seems more responsive and spikey when rested) and out of form (HR is higher because my body is not as efficient with its efforts).
This is one of the reasons I actually stopped using the HRM this year, the descrepancies over time vs. perceived exertion was kind of frustrating to me.