If the farm next door is growing for extraction, they are likely to try and avoid pollination, it's dicey with acreage. Timing and personnel are crucial because it all happens real fast. Extraction requires bud resin.
I don't know a lot about the industry. I would imagine that 40 acres of female only or mostly would only be possible by hyper hybridization, which also means, probably, no viable seeds or not many. Hard to tell with experimental stuff.
If your crop is smaller or has indoor ability, some kind of isolation is advised but strict management will do. With hemp, cross pollination is no issue, and I am beginning to wonder if it even matters if marijuana is adversely affected if it is cross pollinated in the field, as opposed to lab conditions. High grade hemp for CBD extraction is had to differentiate from the other and only by lab testing for the various canabinoids can you clearly identify. The hybrid hemps can run "hot" with THC and cross the line of differentiation.
Lacking the presence of pollinators when it's time, females will sprout pollen pods, like overnight, and it's hard to catch with a large plot. The farm may opt to harvest immediately upon the point where seeds begin to develop, all the properties are present at that point, I think.
And that's what I learned on my summer vacation last year. 
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