Practical Programming in Tcl & Tk, Third Edition By Brent B. Welch
Table of Contents
Chapter 51. Tcl/Tk 8.0
The clock command now implements the following standard convention for two-digit year names:
70-99 map to 1970 - 1999.
00-69 map to 2000 - 2069.
Actually, the ability to parse a date value after 2037 and before 1903 may be limited on your system by the size of an integer (e.g., 32-bits) and the clock epoch, which is January 1, 1970 on Windows and most UNIX systems.