I'll offer a few thoughts, for your consideration, but there are so many things unknown so I'll first state we just don't, and wouldn't, have enough information to determine which way to turn, and what the next step "should" be.

1. How does your barrel feel when running a tight patch through it, or brush if you run a brush in your barrel. If there is not consistent tension from start to finish, it's very possible that specific barrel will not duplicate a published book data points.

2. Brass - can make a pretty big difference if you don't sort brass. A large variance in case volume can result in a wide range of velocities. And neck tension, and...

3. Type of powder - I learned this one through field tests and later it was confirmed by research/reading. I had a 22-250 loaded with H380 - and large rifle primer. All my loads were about 200 fps less than book data - that was also with LR primers. I switched primers to LRM primers, started load work up again, and my loads matched the book data. Through reading later I found several sources that stated ball powders, in general, like hotter Magnum primers to burn clean. Which was 100% consistent with what I experienced. That being said, I matched powder charge-weight and velocity to the book, but did not match published primer. Suffice it to say, since then, I've become much more sensitive to trying different primers when building a load.

4. I encourage you to try this. Take a known load, that is very consistent of known velocity. Set your chrono up, and be very specific to shoot directly over the sensors. Then intentionally shoot over to one side or the other from the sensors. Another way would be to line up 2 separate chrono's - just offset them an inch or two. Not shooting DIRECTLY over the sensors will yield a very LARGE difference in velocity. My point is, it may be as simple as you THINK you are not getting the expected velocity, when in fact you ACTUALLY ARE - due to something as simple as not shooting directly over the chrono sensors. It's a huge difference, and very educational.

5. My final point is probably the biggest. WHO CARES??!! The first couple of years I reloaded cartridges, about 45 years ago, I was pretty tuned in to velocity in my reloading practices. Then I stumbled on an incredibly consistent and accurate load at significantly less than book velocity, or charge. Upon considering what to do about having such a good load at reduced charge and velocity, it came to me that reloading is NOT about velocity as an end all. If your loads are consistent, but slower than published data - why wouldn't you want to stick with that load? Wouldn't you rather shoot a slower load and know exactly where it will hit time after time than chase velocity? If your recipe is tight, accurate, and POI is predicable, velocity is so far down the list of goals. Add to this that excessive pressure is SO dangerous that there is very good reason to be very careful with anything that exceeds published data. It's honestly not worth chasing velocity. Were any of your slow loads extremely accurate? If so - WHO CARES if your velocity is slow in comparison. That type of thinking allows you to reload for the next 45 years, safely.

There is no free lunch when it comes to velocity and pressure. You most likely will not find a magical recipe that is so much better than all the other published data sources and friend experience. Load to accomplish tight grouping, and drop velocity as a measure of performance when reloading - it's dangerous.

In a nut shell, these are just a few things, and there are many more, that may explain the discrepancy you believe to be faced with. YMMV.