To a certain degree.
Short answer stick to a max mAh difference of 400 between cells and try to keep the IR difference to <15mΩ.
That is correct they will be acting as ONE cell. The voltage will be the same on all cells so charging will occur according to voltage not capacity of the cell. You cannot overcharge any cell as long as the pack voltage does not go over 4.2V.
Water in a vessel is an excellent representation of voltage and capacity. It is a crude representation nevertheless you can see in the illustration below we have 4 separate vessels of different capacities. They are being filled (charged) by the Tank. The water (voltage) will seek its own level in all containers. This is how cells will react in parallel with different capacities.
View attachment 26399
If all you have is a conglomerate of different manufacturers / part numbers of cells then in my experience your pack voltages below 3.6V will begin to deviate a bit between packs. In my case the max deviation is about 0.09V This is not a huge concern as long as you monitor it and keep track of any irregularities.
I built my first 14s80p from basically 4 manufactures. Sanyo, Panasonic, LG, and Samsung with 28 different part # as shown here with min, max, and average values.
View attachment 26404
The result was a reasonable Frankenstein pack that performs quite well. Here is a trace of the pack voltage and deviation voltage per pack through the charge and discharge cycles.
As you can see once voltage drops to ≈ 3.6V the pack voltages start to seperate a bit. The purple tracer shows that.
View attachment 26403
My 2nd battery packs are all of the same cell and manufacturer with a mAh difference of ≈300 and an IR difference of <5mΩ
View attachment 26405
The results of closely matched cells is very apparent by the voltage difference between packs during charging and discharging.
In this case < 0.015V through the charge and discharge cycle.
View attachment 26402
Additional information can be found in my thread of how batteries act in parallel.
Another experiment has taken place at the Wolf's PowIRwall location. Previous posts on this subject are at https://secondlifestorage.com/showthread.php?tid=7846 I dragged out my 4p testing rig and decided to test 4 ICR18650-28A cells that had a reasonable IR at ≈ 50mΩ but their mAh testing was...
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