First, the 1841 census lists both Foster and Elizabeth as born in Renfrewshire.
Second, the parochial boards were pretty diligent in seeking out where people were born. This is because where you were born was an important part of determining which parish was responsible for looking after you when you fell on hard times. If abc parish board could find a reason to transfer the cost of relief to xyz parish board, they would grab the chance to do so. So if the poor relief record says Renfrewshire, you can be pretty sure that is right.
The absence of any record of baptism in Paisley doesn't necessarily mean that they were not baptised there. It means that the record, if it ever existed, either doesn't exist or isn't available online.
There are many reasons for this, including
- the parents neglected to have the children baptised
- they were baptised but the parents omitted to have the baptism recorded in the register
- they belonged to a religious denomination whose register has not survived
- they belonged to a denomination that did not practise infant baptism
- the minister omitted to notify the parish clerk
- the clerk forgot to record the event
- the record is in a register that has been lost
- the record is in a register that is not available online, for example Episcopalian, Congregational, Baptist, Society of Friends etc
