Velocity scores are affected by intent, arousal ("psyche up") and fatigue
Velocity scores are NOT some stable, concrete thing that are 100% linear with strength and merely affected by cumulative fatigue levels across a set. Arousal levels and intent, as well as acute fatigue and technique affect the scores. Here is an example from some deadlifts I did a few months ago, with velocity measured by my Push arm band device. Three sets were done with 165 kg (after sets with 90, 130, 145 & 155 kg and some squats and incline press). The first set of 5-reps with 165 kg is solid, but nothing I need to get up for mentally and I rated it a RPE of 8. The first rep velocity is 0.49 m/s, which for trained powerlifters means about ~ 78% 1RM. For the second set, after 3.5 minutes rest, I decided to do 7-reps, so I was more up for it, intent and arousal-wise (arousal is often termed "psyche up" in lay terms) and the velocity of the first rep has jumped to 0.55m/s ~ this is like an instant 3% change in 1RM, so now is this weight 75%1RM? The RPE was only slightly more, 8.5, because I was more intent and aroused to do more reps. The third set I decided to do 8-reps, so I took an extra minute rest to negate some of the acute fatigue which can really affect my tightness off the floor, one of the keys to deadlift success. But on the third set, my first rep was 0.45 m/s, which if I believed in using velocity to predict my daily max (I DON'T), would mean I just lost about 6-7% from my 1RM and 165 kg is now about 81%1RM. But I did 8 reps and the RPE and last rep (8th) velocity is identical to the second set last rep (7th rep). So the RPE is the same, 8.5 because the last rep is the same velocity for both sets. But the first rep is slower because of the fatigue I was feeling at this point of the workout and the effects of the second set. Therefore it can be seen that the fatigue of the session and my arousal levels were just acutely altering my velocities while lifting the same weight. Velocity measuring and monitoring are fantastic, but realise that velocity scores are affected by acute fatigue from within the workout, cumulative fatigue from the day/week/month, technique, and intent/arousal and how close you train to failure (the maximum effort velocity). The key things to remember is that your best rep (which is usually the first) in your heaviest set, is the best predictor of your current strength levels. Here I did three heavy sets, so the best rep was the first rep of the second set, 0.55 m/s tells me my strength level, "aroused". I would say 0.49 m/s would be a normal score with that weight, not "aroused". So my advice is to keep track of velocity scores done with the same weights and under similar training conditions (including arousal levels) to observe if strength changes have occurred, rather than try and predict some daily 1RM from a warmup set. The easiest way to do that is to get a Push device from my website and just start using it in training.