Yes wood of any type can be just about any MC, given enough time and the right conditions. If you lived in arid parts of Arizona or
SPF ... in my climate controlled basement for about 10 weeks ... MC of 11-14% still
the 2×6s that were used to frame our basement walls [5 years old] 10-12%
maple and walnut in the same basement ... 7-9% after about a year.
Your maple was almost certainly drier to begin, that will account for some of the difference in the readings you're getting, and kiln-dried wood (almost always drier than air-dried) is said by some sources* to permanently remain drier than air-dried wood.
Now all the wood here is kiln-dried more than likely, but hardwoods are typically taken to a lower reading than construction-grade softwoods (because it's less important for 2x material to be as dry, it is not merely through impatience or cutting corners).
Does construction lumber stay inherently wetter than other hardwoods, even after acclimating?
Within the limited timeframe we do it at, I'd say this would be nearly universally a yes.
While the common advice is to let wood acclimate in the shop (for weeks or months, depending on who's advising) in reality this often only gets it closer, not actually to the EMC for the location. It's very easy to test this real-world by resawing any board and comparing the readings from the original surface with what was the core of the board. Very infrequently will they measure the same. This is one of the two reasons that re-sawn wood will so frequently warp after cutting, unless stickered, stacked and clamped/weighted, or, wrapped tightly in plastic to prevent it drying.
*Note that this is a contended issue and some heavyweights state that all wood will come to the same EMC given sufficient time. Although there are many anecdotes that suggest this is not the case the exact storage conditions obviously play a major role in how, or even if, this occurs with wood stored in any workshop of any size. Variables include just how dry the environment is (hence the moisture gradient), how consistently dry it is, the amount of air exchange (critical factor in all drying) and perhaps most important of all, the way the wood is stacked (no air space may mean some wood remains wetter indefinitely).
