One of the most telling ones came in the third quarter of last week's preseason game at Chicago.
Bortles got to the line of scrimmage on a second-and-1 play, recognized the coverage, checked from a run to a pass and then found his third option down the left sideline for a 29-yard gain.
Between the pre-snap read, the audible, the in-play progression and the throw, it was a perfect performance by the third overall pick in May's NFL draft.
"We're excited about how he has progressed," offensive coordinator Jedd Fisch said Tuesday. "I think it's a situation now where each day we are just looking for improvement, and he has challenged himself to get better every day. So, really I'm not exactly sure where I expect him to be, so he is doing well for where he is at."
Despite getting repetitions with the first-team offense in practice this week and a planned quarter of work with the starters at Detroit on Friday night, Bortles remains the backup.
At least for now.
Bortles' preseason play has earned high praise from coaches, teammates and fans, but it hasn't changed the team's belief that he's a work in progress. General manager Dave Caldwell, coach Gus Bradley and Fisch want to foster a pressure- and expectation-free environment around Bortles that allows him to focus on refining his mechanics, mastering the playbook and making a smooth transition from a college spread scheme to a pro-style system.
"He just has to continue to build and learn," Fisch said. "He is throwing the ball with a little bit better velocity, maybe using his lower body better. ... He keeps getting better in terms of understanding the offense. His knowledge base is improving, so he can play faster, make corrections on the fly and make adjustments."
Much like he did against the Bears.
Bortles completed 11 of 17 passes for 160 yards in the game, bringing his preseason totals to 18-of-28 passing for 277 yards.
He felt like he took steps forward from Tampa Bay (preseason opener) to Chicago.
"I thought my footwork was a little cleaner," he said. "There are still some things I need to work on and clean up, but I thought for the most part that's been a big emphasis on what I've been trying to do for a while now. So, I thought it was a little bit better, but I still have a long way to go."
Playing with and against starters is the next phase of Bortles' development.
He got about seven snaps with the first-team offense in practice Monday and Tuesday, but will get a bigger test with several series against the Lions.
"Yeah, obviously it's a little bit faster," he said. "It's just a good opportunity to go out there and get that exposure and go see that and get to play against it. In the end, we're calling the same plays and you're running the same stuff. It's just that guys are a little bit faster. You have to adjust to that and get some exposure to it."
The Jaguars are committed to Chad Henne at least to start the season.
Henne has been solid in the preseason, completing 16 of 24 passes for 160 yards and a touchdown.
Henne has said repeatedly that his job is to keep his job, but he also has welcomed Bortles and offered to help him anyway he can — even though he knows the rookie will replace him at some point.
"We're just out there trying to help each other out, competing each and every day," Henne said. "The biggest thing is guiding him along and I just try to help him with the footwork and knowing where to go with the football. He's done a great job. We're both humble and that's what's great about this position."