I will check IGI again in a moment but first decided to check the 1841 Census for the name 'Red'.
It seems to be a legitimate name as the first page begins with names like Alfred then Ann and down to Catherine with all born and residing outside the 'mother Country' of Cornwall.
Next step (doing now) is to check those resident in Cornwall in 1841.
Results:-
Farterrao Red born about 1816 Cornwall living at Stithians
Maria Red born about 1776 living at Falmouth
Richd Red born about 1776 living at Falmouth
That is it.
In the 1851 Census I found no member of the 'Red' family born in Cornwall.
An IGI search on the surname 'Red' in Cornwall produced only 49 results.
A few at Egloshayle and Endellion.
A couple at Ludgvan.
Most at St Ives.
The earliest entry is one of those obscure ones that you see in IGI:-
Petherick Red born 'abt' 1630 of Egloshayle
married 20th November 1652
1st August 1655 we have the marriage of Edeth Red to Thomas Sander at Egloshayle
James Thomas junr married Elizageth Red at Ludgvan 24th June 1766 (confirmed with Phillimore)
8th September 1633 Katherine Redd bp. d/o Hugh Redd at East Newlyn
RED baptisms at St Ives:-
30 Jan 1737 Agnes d/o Thomas and Agnes
15 Dec 1739 Andrew s/o Thomas and Agnes
29 Jun 1742 Elisabeth d/o Thomas and Agnes
30 Jun 1745 Thos. s/o Thoms. and Agnes
03 Dec 1749 William s/o Thomas and Agnes
06 Mar 1756 John s/o Agnes Red
28 May 1786 Elizabeth d/o Thomas and Prudence
04 Nov 1787 Prudence d/o Thomas and Prudence
25 Oct 1789 Mary d/o Thomas and Prudence
21 Dec 1790 Christian d/o Thomas and Prudence
26 May 1793 Thomas s/o Thomas and Prudence (d. 28 Jan 1794)
That's all and there ain't no more.
Comparing the above with your information it is obvious that the IGI entry has been updated to reflect the Gregorian date.
(Damned frustrating.)
I also can find no marriage to an Agnes whether it be Thomas Red or Thomas Bennetts.
There is, however, a marriage at St Ives in 1736 for Thomas Bennetts and Mary Leddra.
Maybe a longshot but it may perhaps be worth having a look at them to see if anything shows up.
A search for a birth/baptism for Thomas Red produced 5 results but all are for the same person.
Thomas Red born 'about' 1712 Stevenage, Hertford.
Each of these entries gives a Marriage date of 31st March 1734 which is about right for the first baptism at St Ives.
But one of these entries provides a brides name - Sarah Clarke.
This is a most peculiar and difficult problem so I am going to 'flick pass' it back to you for now.
And let us see what our intrepid investigators can come up with that may help.