I think timelocal() wants the year to be years since 1900

That would make sense. But the documentation says:

Strictly speaking, the year should also be specified in a form consistent with localtime(), i.e. the offset from 1900. In order to make the interpretation of the year easier for humans, however, who are more accustomed to seeing years as two-digit or four-digit values, the following conventions are followed:

• Years greater than 999 are interpreted as being the actual year, rather than the offset from 1900. Thus, 1964 would indicate the year Martin Luther King won the Nobel prize, not the year 3864.

• Years in the range 100..999 are interpreted as offset from 1900, so that 112 indicates 2012. This rule also applies to years less than zero (but see note below regarding date range).

• Years in the range 0..99 are interpreted as shorthand for years in the rolling "current century," defined as 50 years on either side of the current year. Thus, today, in 1999, 0 would refer to 2000, and 45 to 2045, but 55 would refer to 1955. Twenty years from now, 55 would instead refer to 2055. This is messy, but matches the way people currently think about two digit dates. Whenever possible, use an absolute four digit year instead.

The scheme above allows interpretation of a wide range of dates, particularly if 4-digit years are used.