There are a couple of drafts happening in some of my leagues right now and I noticed that some players show a +1 or -1 in the potential value where it shows their actual/potential growth since the beginning of their creation or the season. (example: from start: +0/+1 this season: +0/+1)

I was curious, is this a trustworthy indication that the player will most likely increase in their potential if they have a +1 and vice versa? I haven't been playing long enough or paid enough attention to have seen what happens either way.

No, it's not an indicator of anything, more likely is a rounding error. I thought I had fixed it but will check it out (could you post a link to one of the player pages in question?)

http://cust64.myfootballnow.com/player/1001

It doesn't show it on his page in the progress tab, but you can see it on the draft board when you click on the player information

I notice this a lot when I draft a player and then immediately change the player's position to something else.