The problem
You are looking at imagery from say the year 2000. You see a highway that is not mapped yet, so you want to add it in. The problem is, you don’t know the start year. You can put in the year from the imagery, and perhaps use the EDTF format to indicate it likely was there already before that. So far, so good.
Now somebody is mapping in 1980, using imagery from that time. Sees the highway, and it’s not mapped yet. (given his filters are set to 1980) This mapper could remove the filters to see if it’s there yet in a later timeframe. But that would be an incredible maze to look at everything that has been there post 1980.
this results in two things:
-it’s hard to map 1980 stuff, because you have to perform that check I tell you about.
-you hold back on mapping stuff, because you don’t know the start date. (which will result in point one being harder)
The proposal
You should be able to map using 2000 imagery without worry. You should be able to set the start date to 2000 and a ‘it’s likely been here before this date’ (which can already be done using EDTF afaik)
Then the 1980 mapper sees all 1980 stuff (in solid like now?) + all these items set with the unclear start date. (slightly less opaque?)
Then the 1980 mapper can do two things: confirm the item has been there in 1980 too, and edit the start date accordingly and set ‘it’s been likely here before 1980’; or add a ‘but not yet in 1980 value’.
In turn the ‘but not yet in 1980’ values would not show up when editing 1980s or before.
these ‘it’s likely been here before date X’ items are only visible before date X on the edit side of OHM, not on the actual public map.
The result
This way one can have more of a peace of mind while mapping I feel. I shouldn’t feel too bad about adding dates to streets when mapping recent history; knowing my edit won’t show up in the roman empire, but also not make it harder for slightly older history to map.
I think this will bring a serious boost in mapping history since 2000 (when imagery is easy to come by)
For example, I now have mapped all rail lines as single track, because I don’t know when something went double track. I don’t know about the station layouts way back then. So I don’t really map it now. But that also means I can’t map current (or relative recent) changes in history.
(I hope my explanation is somewhat clear 
)
I didn’t really want to spam every channel with this idea, thought this may be the best place to have a discussion with the most potential viewers 