The second IC adds (erroneously) "6548 = 6550, Swift in Cat. XI.". Considerable confusion has reigned for more than a century as to the correct identification of NGC 6548, 6549, and 6550. NGC 6548 was discovered by William Herschel in 1786. That galaxy and NGC 6549 were observed by Albert Marth in 1864; and in 1880, Edouard Stephan observed three objects in the area -- undoubtedly Herschel and Marth's discoveries, and most likely an asterism which he mistook for a nebula. In compiling the NGC, Dreyer was uncertain which objects were which, and assigned separate numbers for each of the three "discoveries". However, (per Corwin) recent examination of the area makes it fairly certain that NGC 6550 is a mistaken repetition of NGC 6549 (which see for images). As an example of how confused the situation is, NED equates NGC 6548 and 6549, while HyperLeda equates NGC 6548 and 6550; so aside from the fact that both identifications now appear to be wrong, any data which supposedly apply to one NGC object may actually apply to another, and only the PGC listings (or some similar non-NGC identification) should be relied upon.

No object resembling Leavenworth's drawing exists anywhere near his recorded position. Since his drawing looks like a globular cluster, NGC 6551 is usually identified with the nearest globular cluster, NGC 6522 (for instance, the NGC/IC Project lists them as being the same). But aside from a huge error (more than a degree) in position, that object does not really look like his drawing, so even that identification is uncertain at best, and the most accurate description for NGC 6551, as shown above, would be "lost".

A Seyfert galaxy (type Sy2). Based on a recessional velocity of 7940 km/sec, NGC 6552 is about 370 million light years away. Given that and its apparent size of 1.0 by 0.7 arcmins, it is about 110 thousand light years across. NGC 6552 happens to lie fairly close to NGC 6543, the Cat's Eye Nebula, which is only about 10 arcmin to its west (as shown in the last image, below). However, since NGC 6552 is a distant galaxy, and NGC 6543 is only a few thousand light years away, their juxtaposition is merely coincidental.

Per Dreyer, NGC 6598 (= Swift I (#88), 1860 RA 18 09 50, NPD 20 58.6) is "extremely faint, pretty small, round". The position precesses to RA 18 08 52.2, Dec +69 03 19, just over an arcmin to the southwest of the galaxy; given the galaxy's size and proximity and the lack of any other nearby objects, the identification is certain. Based on a recessional velocity of 8310 km/sec, NGC 6598 is about 390 million light years away. Given that and its apparent size of 2.0 by 1.4 arcmin, it is about 225 thousand light years across.