There is actually no P-72A in SCWPM as you can see. If banknotemuseum uses a wrong reference we should not. I agree there is a difference in the name of the country and that should be reflected in the description. But listing a note in this manner is the main problem.
To Allexis: The Present Issues 25th ed. (2019) of SCWPM under SRI LANKA explains and lists P# 72A.
"Central Bank of Ceylon
Issues After May 22, 1972
King Parakramabahu Series. The difference between the Ceylon 72- 80 bank
notes and the Sri Lanka 72A-80A bank notes is the character that is located
on the first line of text underneath the bank's name. The character is only
present on the Sri Lanka notes. 72A 2 Rupees VF UNC
1973; 1974; 1977. Light brown on lilac, light green and blue
underprint. Statue of King Parakkrama at right. Back: Pavilion.
Watermark: Chinze. Printer: BWC.
a. Signature N. M. Perera and W. Tennekoon. 21.8.1973;
27.8.1974.
2.00 6.00
b. Signature R. J. G. de Mel and H. E. Tennekoon. 26.8.1977. 1.50 5.00 For notes issued before May 22, 1972, see Ceylon #72."
So 72-80 pages under Ceylon, 72A-80A pages under Sri Lanka.