First, the fact that DFWs runways are "very long" doesn't automatically mean your MTOGW for takeoff on a particular runway, on a particular day is going to be the max certified weight for your aircraft. Factors such as winds, temperature, assumed/flex temps, 10/20 % derated thrust for some aircraft, obstacles, flap settings, etc. may not allow takeoff at max certified weight.

Second, each airline has specific methods they use to compute performance. Mine doesn't use ACARs. We use a program incorporated into our EFB and compute all the data ourselves, both for takeoff and landing. My previous aircraft at the same company used quick reference data in the QRH for landing distance.

Third, information received from whatever source(s) an airline uses may be presented very differently. Assuming we all can decipher the end product you receive and help you with your questions is a big assumption. Along those same lines, your assumption that "everyone" gets the same information when computing landing distance isn't valid. On my a/c, we input landing weight, ATIS information and runway condition, max or idle reverse, MELs/CDLs. The output is landing distance for each autobrake setting and XW/TW components. We don't get unfactored blah blah.... 60% factored whatever and start doing math. It's one number for a particular set of conditions and autobrake setting.

I think the recommendations that you contact your training/standards department are a good start. Having a solid working knowledge of the performance information provided to you by whatever method you use is pretty important when you start getting close to the edges of the envelope dealing with windshear precautions, cluttered takeoffs, runway shortening and obviously landing under less than optimal conditions.

Not so fast, some operators require the factored distance for actual landings.

Yes but the factored distance isn't the "stop within 60% of the LDA" used to release the aircraft.

Your structural max takeoff weight is 84,500. The 79,000 is probably max landing weight plus fuel burn. Was your fuel burn about 3,900? If you took off at a higher weight, you would be overweight for landing. The 74.7 is probably based on a FLX temp (although flaps 8 vs 20 could be an additional factor). If you were to select NO FLEX, AeroData (ACARS) would probably come back with a higher weight. Entering a higher weight would also likely give you good data with a resultant increase in take off N1 (Lower flex temp or even full thrust)

What might be causing some confusion is that there are several different takeoff weights listed in different places throughout a release:

Max structural: 84500 for CRJ 900
Manufacturers performance baseline (my term): often several thousand pounds higher than even max structural
Max flight plan: The most you can takeoff with (considering planned fuel load and burn) and not exceed other weight limitations (usually landing weight, but I'm sure a scenario containing ramp weight or ZFW could be created)
Planned takeoff: Usually right at your planned weight, often with an extra line for 1000/2000# over that. This is where you get your numbers for takeoff if your ACARS is inop.

All of these will make some reference to MAX, TAKEOFF, and WEIGHT, but they are not the same.

In your initial scenario, it is possible that 79,000 was your max flight plan takeoff weight (for max landing weight) and 74.7 was your planned takeoff weight. Maybe there was another line for plus 1000#. Even if there wasn't, you could call dispatch and have them send you a new release with higher numbers.

Again, this is a situation that requires attention to detail. Your QRH most likely references Actual Landing Distance. In that case you would determine Actual Landing Distance (probably from your speed book) and add the 20%. Minimum Landing Distance is a different number (without looking it up, I believe it is a factored number used for dispatch legalities). However, some airlines also require you use a Minimum Field Length number to land (ie, you can't use Actual Landing Distance for normal operations). Using the QRH waives that requirement in most cases.

Best advice: Read the related sections (Performance/Release/Loading/Etc) of your GOM/FOM and your POH/FCOM. Read the QRH items in question. Read them all in detail. Small words make big differences. Also might not hurt to ask other pilots. Like has been said previously, this should have been covered in initial. It will definitely be covered in the upgrade oral/KV.

If any YV Pilots here can access ASAP report from last September re: a flight to SBA that diverted because of a 20% penalty per QRH and the unsuing argument with dispatch as to whether they could have landed.... that’d help clarify things I think.
I’ve asked 2 check airmen, gotten 2 different answers.