Bearings have different suffixes appended to them because they differ significantly. Do not simply substitute a bearing with the same number if the suffix differs. This may or may not be a problem, but you need to understand the difference(s) before you make that change. For an example, we will use a cylindrical roller bearing, common to Italian transmissions.
The NJ210E is used in the older Pasquali transmissions and is labeled as bearing 8473 on the transmission parts diagram. This is a typical, high quality cylindrical roller bearing capable of carrying some serious load. It is a 50 mm ID x 90 mm OD x 20 mm deep bearing.
Mistake One: Replacing by size. Since the NJ210E is 50 x 90 x 20, a common mistake is to replace the bearing with a 6210 bearing. This is a deep groove ball bearing and while it's a capable bearing, it won't take the pressure or thrust of a cylindrical roller bearing. These are a different type of bearings and are used for different purposes - they are not normally interchangeable with each other.
I say normally not interchangeable because in some cases, the added strength and carrying capacity of the NJ210E could possibly take the place of a 6210.
Mistake Two: Replacing by bearing type and disregarding the prefix or suffix. In this example we will use a ball bearing as an example first. When purchasing a 6202 replacement, you will often be given a 6202-2RS bearing. A 6202-2RS bearing is the same as a 6202 except the 2RS suffix means it has a rubber seal on each side of the bearing. If the bearing you are replacing is simply a 6202, then you take the new bearing and remove the seals from each side. You cannot substitute a 6202 for a 6202-2RS because of the missing seals. A sealed bearing is sealed to keep lubrication in and contaminates out. Transmission bearings will not have the seals on them because they are bathing in transmission oil for lubrication.
With a NJ210E, you need to understand what you are dealing with. NJ means that the bearing has two integral flanges on the outer ring (holding the rollers in place), but the inner ring has only one. An NJ bearing is designed to locate the shaft axially in one direction. This means that it can only accommodate axial displacement in relation to the transmission case in one direction only. In other words, make sure to replace the bearing in the same way it came off - it's directional.
The NU210E, is exactly the same bearing without any inner flanges. This means the bearing is designed to locate in both directions, but that could be a bad thing if the transmission isn't designed to accommodate it. In other words, don't substitute a NU210E for a NJ210E.
The E suffix refers to the rollers, the size, the number, the capacity, etc. SKF bearings using EC as part of the suffix means the bearing has been optimized using more and/or larger rollers with modifications made to the roller ends / flange contact. The suffix CV means the bearing is full compliment (flanges both sides top and bottom) and will not allow axial displacement.
If an N follows the suffix, it means the outer race has a snap ring groove, if NR it includes the snap ring.
If a J follows it means it has a stamped steel cage, roller centered. If a P follows it, it means the cage is glass fibre reinforced, roller centered. So a NJ210ECJ and a NJ210ECP can be both used for application in the Pasquali transmission, where bearing speeds are less than critical and the cages would be both compatible to the environment. There are no fewer than 15 cage styles that can lead to the confusion (bronze, polymer, etc.). So as an example, a NJ210E-TVP2 is a caged bearing which would be better not to substitute without a knowledgeable bearing tech commenting on it. It might be okay, it's just I don't know that. Always seek out the advice of a bearing technician if anything differs.
The idea here is not to confuse you or make it more complicated than it is, but to understand a bearing is not a bearing, is not a bearing. Working with a good bearing supply house is important if you don't understand bearing names and what the prefixes and suffixes mean. If your bearing guy is substituting without asking questions about application and what it's for, you might be better to continue looking for the right bearing(s) somewhere else. Bearings are very specific and should not be substituted without knowing the consequences.