From our web page:

"An "errata sheet" was available for the First print; unknown where these sheets came from (since the books were not shrinkwrapped, it is highly unlikely they came with the book purchase).  Most of the errata mentioned on the sheet were corrected with the Second print, so we surmise it was released sometime between Dec 1977 and May 1978.  More info is needed."

So no, they didn't originally come with the hardback (they would have fallen out).  A presence of one could inflate the value, yes, but as it would be very easy to counterfeit, take extreme caution.

Foul

The errata sheets rarely come up for sale by themselves.  Many of them were tossed or lost over the years.  When they do come up, they sell for a considerable amount.  Most of the ones that survived were inserted into the pages of a Monster Manual or taped/stapled to the front or back of the book.

I would agree with the second part of what Mars wrote, namely that MM errata sheets sell for around $500 give or take. I think I have 6 1st print MM's and four of them have errata sheets.

I have six and three. :)

[lol] .. sorry, I couldn't help myself :)

Actually, I am going to sell one. Would people here advise selling the errata with the Monster Manual or separately? (my general preference is usually for 7-day ebay auction listing, but happy to be persuaded otherwise)

FoulFoot wrote in 1e 1st print Monster Manual with and without Errata:From our web page:

...it would be very easy to counterfeit, take extreme caution.

Foul

I am a yellow belt in printing. I know just enough to be dangerous to myself and others, so I may be wrong; but though it would be easy to counterfeit these for ebay photos, it would be a challenge to print these as they were in the 1970s. Toner stands out under 20x. It's all splotchy with rough edges. It would take some work to set up a press that produces the same result. Right?

red_bus wrote in 1e 1st print Monster Manual with and without Errata:[lol] .. sorry, I couldn't help myself :)

Actually, I am going to sell one. Would people here advise selling the errata with the Monster Manual or separately? (my general preference is usually for 7-day ebay auction listing, but happy to be persuaded otherwise)

The pair sold for $1591.13     I made you an extra $442.61.    You're welcome  :-)

I have two, one with the errata sheet, one without.  So 50/50 for me I guess.

I'm not entirely sure, but it follows how the woodgrains were done.  I highly doubt the first copies sold had the correction sheet in there.  My second print woodgrain does.  I have seen some first print woodgrains have the correction/errata sheet included in auctions over the years.  In terms of the Monster Manual, my guess is not all inventory of the first print were sold when the data for corrections was assembled and I'm assuming here that TSR added the loose page for the remaining stock before the second printing came out.  When they did and where it sold was another matter.  However I do think the errata/correction sheet came early.  I have a first print of Unearthed Arcana for example and it was quite quickly after its release Dragon magazine had an errata sheet for that book.  In terms of increasing value, I think it boils down to as collectors who wants rare ephemera that was corrected in later printing.  It's a curiosity piece that TSR published for a small time window before stuff got corrected in later printings so I think that alongside the first printing of the Monster Manual itself makes the value rise.  As I said above, I have two, one with and one without.  Curiously the one without it has more wear and tear (not bad shape, but definitely used) whereas the copy I have with the errata sheet looks new as in hasn't been used.