What does a resistor value of "NOM" mean?
These were hand drawn and you usually have to check around the first few sheets to understand the syntax.
Check out NASA Drawing 2005904.
NOM means NOMINAL.

As for the NOM values.  These refer to the actual part numbers.

R3 and R4 are 22kΩ, 1/2W resistors, Part No 1006760-64.
R1 and R2 2%, 1/4W resistors that are referenced in the table, Part Number 1006750.
Looks like 1006760 is the generic part number for 1/2W resistors and 1006750 are 1/4W resistors.  These resistors are in bins and these boards were probably assembled by hand.

With Part No 1006750-XXX referring to different actual resistors for different part lists.  Different versions for different iterations of the design.  As in 126 is bin 126 in the parts inventory.
Part No 1006750-126 to 1006750-129 are (probably) 1% resistors towards the end of the design period.
So R2 is Part No 1006750-25, which is a 510Ω resistor.  Similarly R3 on the sheet you reference is the same part number.


My initial answer is sort of right.  The parts in the Table do not show the design evolution but are possible alternatives (nominals) to be verified by testing.
From Apollo Block II and LEM - Computer Design Review

8.3.1 Selection of Nominals (A)
In the build-up of several of the computer modules certain nominal values are selected in order to make the circuit work. This technique requires that a group of parts be supplied to the person building up the unit. Questions that arise in this area are concerned with the criteria being used for the selection of the nominals and the control of the piece parts which are not used. The circuits are most often tested at room temperature, presumably using criteria which will guarantee that the design is adequate at the temperature extremes. The review has not been complete enough in several of these areas to indicate whether this is a satisfactory procedure or not.  In the case of one resistor value in the A circuit of the interface module, it has been determined that the range of nominals is inadequate to account for the range of parameters of associated components of the circuit which are presumably not selected.

These are engineers who are sending a computer made from NOR gates into space to land men on the moon.  They are going to test the crap out of it to minimize failure of key components.  No simulations, but physical variance of key components to ensure mission success.
R3 is in module A.  If you look at image for R3, the first 18 lines (390Ω to 2000Ω) appear to be darker than the rest (270Ω to 360Ω), which confirms the quote.  These are all the 10% resistors from 270Ω to 2000Ω.  The list was modified to add more alternatives for testing.
The last 4 entries (285Ω to 375Ω) may represent the refinement of nominal values as tests were conducted.

The envelope dimensions called out for the computer are not specified
as maximum. The dimension called out is 6.00 inch. The nominal
computer dimension is 5.996 inch, and if there is any internal pressurization at all it will exceed the 6-inch value.

NASA's use of nominal is clearly normal operation or expectations or tolerances or alternatives.