Very hard to know what the right move to do here as there's a multitude of different factors that work into the scenario, and each scenario is different. Is it open country? Timbered? Foot hills? Broken country? Rut stage? ... etc.
Take this with a grain of salt and this response is just based off of the information you gave and MY interpretation.
"The slow play worked and got him fired up but he seemed reluctant to leave his cows. It did sound like he closed the distance by 50-100 yards at one point but we couldn’t get him to commit. We were on the bull for an hour and he bugled 15-20 times but eventually stopped responding. I’m thinking I might have done something wrong like maybe getting too aggressive too quickly."
It's not that you messed up using the slow play, it worked and the bull came in... but being too far away from the bull / herd is the main issue (setup). But in this case there's a private line boundary, so you are physically limited to how close you can get to the herd as they were on private.
The slow play works best if you can get in close, close, and often closer than what you think is close enough. Many people feel like they don't want to push too close in fear of busting the elk out (obviously use some sense here). But It often leads to this exact scenario of the bull being interested and pulling towards your direction, but never making it making it into your bow range because you felt like you were too close. The biggest thing I would take away from this encounter is, what if there wasn't a private line boundary? How would you have setup? You know that the bull came 50-100 yards towards you, so make sure you setup next time accordingly such that when a bull pulls towards you, it's in your bow range. Great lessons can be learned, when things don't work out.
"We tried working the bull again the next morning and he was much less responsive and had also moved bedding locations and was closer to 400 yards away and across a drainage. If a bull gets slow played once and doesn’t come in, is it safe to assume he is much less likely to respond later on? We gave him a rest for a day and heard him and another bull in the same drainage this morning and waited for them to bed. We got down between the 2 bulls and tried the slow play at around 10am. It was crickets. I’m guessing I educated these elk."
Again, multitude of factors come into play. Elk move, they're wild animals, they're not going to just sit in the same spot every day. While pressure can play a role in where they go, for the most part bulls are going to follow / go where the cows are.
It is still fairly early in the season. Remember it is ONLY Sept. 6th, we are still in pre-rut stages, it's hot out with it being 90+ degrees in many areas, many of the bulls are just establishing their harems. Often many of the bulls running with the cows this early will be smaller bulls, but a LOT of bulls will be coming in and out to check out the cows and leave since they know nothing is in heat yet. Or they'll hang around and bugle to attract other cows to join the harem. Do you want to be yelling outside when it's 90+ degrees out mid day and nothing is happening? Same with the elk. Once it reaches higher temperatures they just want to stay cool and bed, which is typically around 10/11 am. I wouldn't say you educated them, maybe they just know nothing is happening and aren't willing to move? Maybe you weren't close enough to either bull and they did come in? But sometimes the elk don't come into the slow play, *SURPRISE* they're wild animals... If it worked every time, wouldn't everyone kill and elk every year?
Regardless, sounds like you're having a great start to the season! Keep putting yourself out there and learn from opportunities that didn't pan out accordingly and you'll eventually get it done. It's only going to get better from here on out! Cheers to a great September and chasing elk!
*PS*
I hope all is well
@ElkNut1! Hoping to hear from you soon and about your season!
