Sometimes a woman's maiden surname and previously married surnames will be used interchangeably in the baptisms and burials of her children. For example:

In 1794, Susannah Scott married Thomas Robson in Newcastle and had several children by him, all christened at Lamesley in Chester-le-Street district. Note first how the father's name (and probably the mother's birthplace) is recorded wrong in the 1799 baptism, and note how sometimes Susannah is called Robson and sometimes Scott:

• 14 May 1797 Hannah Robson, of Eighton Banks, daughter of Thomas & Susannah
• 7 Jul 1799 Thomas Robson, born 31 May 1799, 3rd child, son of John Robson (native of Eighton Banks) by his wife Susannah Scott (native of Eighton Banks)
• 2 Feb 1801 John Scott Robson, of Eighton Banks, born 11 Jan 1801, 4th child, son of Thomas Robson (quarryman, native of Eighton Banks) by his wife Susannah Scott (native of Dents Hole, All Saints)
• 2 Sep 1804 Joseph & Benjamin Robson, of Eighton Banks, born 24 Jun 1804, 5th children, twins of Thomas Robson (quarryman, native of Lamesley) by his wife Susannah Robson (native of All Saints, Newcastle)

The following year, Thomas Robson apparently died, as there is this burial at Lamesley:
13 Nov 1805 Thomas Robson, of Eighton Banks, age: 39, died 11 Nov, quarryman

In January 1807, Susannah Robson married John Smith at Lamesley and had the following children by him - note how her surname varies:

• 15 May 1808 Thomas Smith, of Eighton Banks, born 8 Aug 1807, 1st child, son of John Smith (pitman, native of Morpeth) by his wife Susan Robson (native of All Saints, Newcastle)
• 15 Oct 1809 William Smith, of Eighton Banks, born 27 Jul 1809, 2nd child, son of John Smith (pitman, native of Morpeth, Northumberland) by his wife Susanna Scott (native of Heworth)
• 20 Oct 1811 Henry Smith, of Eighton Banks, born 13 Aug 1811, 3rd child, son of John Smith (pitman, native of Morpeth, Northumberland) by his wife Susanna Robson (native of Dents Hole)

Even though the clerics were supposed to record the mother's maiden surname in 1798-1812 baptisms, you cannot always assume they did it correctly. Sometimes they may have recorded her prior married surname, or even her current married surname. You have to follow up with marriages to find the truth.

Another interesting thing to note here is that the number of the child refers to the father, not the mother. That is, Thomas born in 1807 was the 1st child of John Smith, but he was at least the 7th child of Susannah Scott Robson Smith - but that doesn't show in the record. Conversely, if a father is listing his 11th child, you can't assume that he has been married to his current wife for at least 10 years - she may be his 2nd or 3rd wife, having her 1st child, but you can't see that from the baptism record. In a very few lucky cases, you may see something like "2nd child by his present wife" or "1st child by his 2nd wife".