Also the naming: in ED it is 51 Pegasi 1 and all the sources state 51 Pegasi b (you could also think about using the names, in this case Dimidum). Or are letters and numbers both possible for naming planets in astronomy and there is no right or wrong?
There are two different, and opposing, systems of nomenclature at work here.
Real-world exoplanets are "numbered" using letters, starting with lowercase "b", in order of their discovery. Since we are not in a position to completely and thoroughly explore another star system, this is a reasonably logical way to go about it as it saves having to renumber everything when new inner planets are discovered, though it does mean that for many star systems, planets may well be "numbered" out of order. For example, if we discover another planet in the 51 Pegasi system, a small rocky planet in a very close orbit around the star for example, it wil be named "51 Pegasi c". But this would mean that in the "system map view" of the 51 Pegasi system, planet c would be in orbital position number 1, with planet b in position 2. Apparently the agreed-upon real-world nomenclature for exomoons is to give them roman numerals, again in order of discovery, though the system hasn't been impemented yet since no actual verified exomoons have been discovered yet. Thus, if two moons were found around Pegasi 51 b, the second one found would be Pegasi 51 b II - whether it was closer or further than moon I would be irrelevant.
ED uses a version of the standard sci-fi planetary numbering system, where stars are given capital letters beginning with "A", planets are then given numbers, beginning with "1", in order of their distance from the primary star. Moons are given lowercase letters, beginning with "a", in order of their distance from the planet they orbit. So in ED, that hypothetical second moon in 51 Pegasi would be called "51 Pegasi 2 a" (or "2 b"). You obviously cannot use this system unless you have reasonable confidence that an entire star sytem has been thoroughly explored and all planets have been detected. Note that ED "cheats" here, when you're out exploring: the planets always have fixed numbers, that do not change if you haven't discovered all the planets yet. So in a partially-explored system, you might have planets 1, 2, 4, 7 and 10 discovered and named - we magically know exactly where the "missing" planets are and what their names/numbers are, even though no-one has ever detected them!
You obviously cannot use both systems of nomenclature in the same universe, as that would cause confusion, especially as ED only shows capital letters in many instances. "51 PEGASI B" (with capital letter B) would be the name of a star, not a planet, using the standard ED nomenclature. So all the real-world planets placed into ED have been renamed or re-numbered to fit with ED's nomenclature. If you look in the TRAPPIST-1 system in ED, for example, you will notice that all the planets there are given ED-style numbers, rather than their current letter designations. The Earth-like world in ED known as "TRAPPIST-1 4" is the planet known in the real-world as "TRAPPIST-1 e".