Possible formats (index.meta Rara):

Blank wird ignoriert:

"1692" 			= "1692"
"1719-1720" 		=  "1719-1720"
"[um 1690]" 		= "1690"
"1605 - 1608" 		= "1605 - 1608"
"1672/1673" 		= 1672-1673
"1769 / 1770" 		= "1769-1770"
"1774, 1775, 1777"	= "1774,1775,1777"
"1794/95" 		= "1794-1795"
"1841-42" 		= "1841-1842"
"2. Haelfte 17. Jh." 	= "1651-1700"
"2. Hälfte 17 Jh." 	= "1651-1700"
"18. Jhd." 		= "1701-1800"
"[ca. 1505]" 		= "1505"
"before 1695" 		= "?-1695"
"ca. 1770" 		= "1770"

Zum Testen:
library/9UM0QW10: 1665
library/3S14G2H2: [1681]
library/YTQVS0WC: 1798/1799
library/0TPK0MMX: 1769 / 1770
library/Q459N3Y6: 1764-1767
library/R285R3N3: 1739 - 1741
library/FV97R8BR: 1841-42
library/9YVRFETK: 1656/57
library/38Y6XYYH: 1794/95
library/7QAAWG5N: 2. Hälfte 17. Jh.
library/U7NRW95K: 2. Haelfte 17. Jh.
library/A87YTC26: [18. Jhd.]

library/F3R4ZCKT: 1774, 1775, 1777

als literal lassen
library/DKSKTVY8: an 7 [1798/99]
library/NP4N2P48: before 1695
library/H0QBVY45: ca. 1770
library/PWMB4GY8: [um 1690]
library/BMQXTH27: [um 1690]
library/XEW08DBU: [ca. 1505]