Got my thinking hat on

Another (!) way of checking for children is to check for deaths where mother's maiden name may have been included in the indexes on Scotlands People. There is this death showing on SP:
1990 EVELYN JEAN WAT. MALCOLM - mother's maiden name ROBB - other surname HOUSTON, age 82 in STRATHAVEN, SOUTH LANARKSHIRE
The problem with the death indexes for women on SP is that two surnames are given, maiden name and married surname but you don't know until you look at the entry, which surname is which.
However, checking marriages there is this entry:
1935 ANDREW DAVID HOUSTON and EVELYN JEAN MALCOLM in HILLHEAD, GLASGOW/LANARK ref. 644/13 0560
As I thought, the cut off for viewing images for marriages in 1934 - this one is showing as needing to be ordered.
Monica