From the parish records, this is the entry supplied for the baptism of George 
Douglas, son of Donald and Isobell Douglas:

   Douglas George lawful Son to Donald Douglas & 
           Isobell Douglas in Lybster was bap
           tized 22 March- witnesses David Ag
           new & Christian Douglas there --

This microfilm page image has no year listed.  The previous image on the 
microfilm tape is marked as page 19.  This page contains the year 1777 so it 
would be reasonable to assume that the page after it is also for year 1777.
Or would it?

There is something wrong with this.  Donald and Isobell Douglas were married 
on 03 Mar 1778 according to the LDS IGI, which is a year after George was 
baptized.  Back in these times premarital births were not as acceptable as 
they are today.

So I went and located the dates of marriage using the LDS IGI for all parents 
on this page and all except one (Simson's) are later than the 1777 baptism 
date.  And for that one, the birth is only 5 months after the wedding.

  David Gun and Katharine McKay married 04 May 1784 Latheron
    Elizabeth Gun 04 Mar 1777

    James	14 Jul 1775  <--
    Elizabeth	04 Mar 1777  <--
    Donald	13 Dec 1778  <--
    Robert	10 Mar 1783  <--
    Isobel	05 Mar 1785 
    William	25 Nov 1787 
    Marcus	20 May 1791 
    David	10 May 1794 

  James Simson and Helen Calder married 14 Oct 1776 Bower
    Robert Simson 04 Mar 1777

    Robert	04 Mar 1777 <--
    Isobel	18 Aug 1781

  Alexander Murray and Margaret Swanson 27 Feb 1779 Halkirk 
   (by fornication) 
    Starachan Murray or Swanson 14 Mar 1777 <--

  William Sutherland and Janet Swanson married 12 May 1778
    Barbara Sutherland 08 Mar 1777 (also 01 May 1777)

    Barbara	01 May 1777 <--
    Sidney	05 Jan 1781
    John	16 Apr 1786
    Katharine	24 Feb 1788
    Isaac	08 Aug 1790
    Jean	18 Sep 1791

  John Gun and Jean Elder married 07 Jan 1780
    Donald Gunn 15 Mar 1777

    Donald	15 Mar 1777 <--
    George	27 Oct 1782
    Alexander	23 May 1785
    William	12 Sep 1787
    Janet	17 Dec 1792
    Mary Lee	19 Jul 1804

  John McBeth and Katharine Campbell married 18 Dec 1778
    Donald and David McBeth 17 Mar 1777
	
    Donald	17 Mar 1777 <-- twins
    David	17 Mar 1777 <--
    Katharine	       1783
    Janet	06 Apr 1786
    Janet	30 Sep 1787

  Donald Douglas and Isobel Douglas married 03 Mar 1778
    George Douglas 22 Mar 1777

    George	22 Mar 1777 <--
    Elizabeth	22 Dec 1778
    William	29 Mar 1784
    Helen	30 Dec 1786
    Christian	04 Mar 1790
    Alexander	21 Nov 1791
    William	08 Sep 1796

  William Gray and Christian (Myrray?) married 09 Jan 1789
    Janet Gray Mar 1777

    Janet	   Mar 1777 <--
    Christian	25 Apr 1777 <--
    Alexander	22 Apr 1781

Note the Murray child "Starachan" was born by fornication and not by married 
parents.  That's how premarital births were recorded.

If we look at the Canadian census records for 1850, we see that George was 
listed as 40-60 years old.  If he were born in 1789 and the census was taken
before March, that would put him at 60 years old.

The 1852 census lists him as 73 and his wife as 60:
  26 Geo Douglas     Mason     Scotland   FCS       73  M
  27 Jennet Douglas            Scotland             60  F
That would put his birth year at 1779.

The 1860 census lists him as age 77 on his next birthday which would put his 
birth year at 1784.  [The Noel book also lists him as "a widower of seventy-
seven in 1861" which I assume is based on the same census information.]  What 
if that age should have been 72 and not 77?

If all the dates of marriage (above) are correct, none of the children could 
have been born before 1790.  However, I'm not so certain about the marriage of 
William Gray so it could have been 1789 or later.

If we look at just the children for Donald and Isobel Douglas, he couldn't be 
born in 1784 since his brother William was.  And he couldn't have been born in 
1790-1792 due to the births of siblings Christian and Alexander.

It is my opinion that the images were out of order when they created the tape.  
If you look at the top of the image, you see a page number which may have been 
mistaken as 20 but seems to be three digits, like 201.  So let's say the page 
should have been March of 1789 instead of March of 1777, that would mean there
were 180 intervening pages over the span of 12 years (144 months). That would 
work out to an average of 1.25 pages per month, or 10 births per month if you 
record 8 births per page, which seems reasonable. 

With the 1852 and 1860 census discrepancies, I think George may have misstated
his age perhaps to have some fun.  From Noel's book we see that he is a little
mischievous.

This could use some more investigation but I'm thinking 1789 would be the best 
choice for George's year of birth, and for all the other births on that same 
page since there are no sibling conflicts at that date.

Does anyone have a photograph of the graves for George and Janet? 

Reference: 
  Title: Parish registers for Halkirk, 1770-1856
  LDS tape 0990521