Two central air proposals can look alike on the first page and still describe two different houses. The part that separates them is the load calculation behind each one. That calculation is the sizing note. It is where you can see whether the installer looked at your house or simply matched the old unit.
What the sizing note should reflect
A proper note comes from the house itself: how much of it is insulated and how well, the size and orientation of the windows, the ceiling height, how much air leaks through the outer shell, how many rooms are conditioned, and what the ducts are like. The capacity of the old equipment is a fact about the old system. It is not a sizing method. If a note says the new unit matches the old one, ask what it was checked against.
Questions to put to each installer
Was a load calculation done for this house, and can you see it? Which method did it use? What did it assume about windows, attic insulation, and air leakage? Did anyone measure the ducts, or only look at them? Does the note say what it left out? If the windows changed or a room was finished since the last calculation, does the new note account for that?
Compare the assumptions, then the equipment
If two notes assume different houses, the proposals are not comparable, even if the equipment names match. Put the two notes side by side and mark each place they disagree. Then ask each installer to explain the disagreement in plain terms. A clear answer tells you something about the work. A vague one tells you something too.
Read the efficiency labels as listings
Efficiency ratings on the equipment label describe how the unit performs under a test. They do not say how the unit will perform in your house with your ducts. Treat the label as one line of information and the sizing note as the rest. The planning dates and typical service life for this equipment are on the Central Air Conditioner page, which is the place to check timing, not a ranking of makes.