It is related to packing.
The BC847C has these two "orderable part numbers":

As you can see, they are the same component in the same package (SOT23), but they differ by packing:
Another example, for the NXP CLRC 633, the datasheet lists these references (and more):

As you can see, the first two are both CLRC66301HN
, both HVQFN32, but one is delivered on one tray, with an MOQ of 490 pieces, while the other is delivered as 5 trays, and the MOQ is 5 x 490 pieces.
The same applies for the next 3 which are all CLRC66302HN
, all HVQFN32, but delivered as either 5 trays (MOQ 5 x 490), 1 tray (MOQ 490) or 1 reel (MOQ 6000).
Some retailers/distributors will sell the components in smaller quantities (they buy the larger reels/trays from the manufacturer and then pick the right quantities from each order or cut parts of the tape), while others will sell only the full trays/reels.
Depending on how many you need and any requirements for production it may or may not matter.
In the case of your Mouser link for instance, they order the 235
version, but allow you to buy either the full reel (10K pieces) or cut parts of the tape from 1 single component. They also have the 215
version, available as full reel (3K pieces) or cut tapes from 1 single component. If you need smaller quantities, it shouldn't matter which one you order, in this case the tape is exactly identical except for its length. You may end up with two different prices for exactly the same component based on whatever rule they have to compute the per-unit price from the full reel price/quantity. Here the difference is very small.
On a final note, the two links you provided point to two actually different references (BC547C and BC547CW) which are actually different components, with different packaging (SOT23 v. SOT323) and different characteristics (different \$P_{tot}\$). So the number after the comma (probably) doesn't matter, but the reference before it does!