Combined X-ray image from Chandra and XMM-Newton of RCW 86. Low energy X-rays are in red, medium energies in green, and high energies in blue. RCW 86 was created by a star that exploded about 2,000 years ago. RA 14h 45m 02.30s Dec −62° 20′ 32.00″, observation date: June 15, 2004. Credit: Chandra: NASA/CXC/Univ. of Utrecht/J.Vink et al. XMM-Newton: ESA/Univ. of Utrecht/J.Vink et al.
...that the first extrasolar X-ray source may have been the diffuse X-ray background. The first Aerobee 150 sounding rocket flight that apparently discovered Scorpius X-1 may have occurred on June 12th or 19th, 1962, and may not have been able to resolve Scorpius X-1 from the Galactic Center as the X-ray detector on board was designed to detect X-rays from the Moon.
...that as the constellation Serpens is actually divided into Serpens Cauda and Serpens Caput, Serpens X-1 is in Serpens Cauda and Serpens Caput was perhaps ignored.
...that Cepheus X-1 is actually in the constellation Cassiopeia.
...that some X-ray sources although initially detected as the first X-ray source in a respective constellation may not have received the designation X-1 as they are diffuse sources, contain several X-ray sources within the celestial object, or occupy area in two constellations. The Large Magellanic Cloud (LMC) is in Dorado and Mensa and contains many X-ray sources. Although established as the first X-ray source in Dorado, the LMC was never designated as Dorado X-1. It was first detected on October 29, 1968.
...that an occasional source such as Triangulum Australe X-1 was designated as the X-1 yet another source in the same constellation had been detected earlier and confirmed prior to its detection. The same may have happened to Orion X-1.
...that Carina X-1 (Car X-1) may have been a misprint for Cir X-1.