The issue of pressed notes comes up several times at every coin show and it is a significant and growing issue with collectors, and properly so.
I have seen many types of pressing. There is the simple pressing of being in a book ( an old & tired excuse most of the time ); a light pressing with water only ; and the Grand-Daddy press and wash with bleach, leaving the tell-tale odour. Good heavens, now we have 'grades' of pressing !
One of the questions posed was that of value changes due to pressing. If the pressing is light and there is no other processing like bleaching, trimming, erasing etc the I normally discount the note 15%-20% both at buying and selling.
Detecting pressing seems something of an art that takes practice. I sometimes miss it, again both buying and selling. I have competent collectors show me notes I thought were original and, on second look, were indeed pressed. So too the reverse with some insisting a note offered as pressed was indeed original - that is rare ! In general, practice will give you 'the eye' to see the un-natural flatness, the absence of embossing, etc. Issues vary in characteristics so that knowledge is important too; eg, the absence of ripples on the signature/serial number lines of Devil Face issues is a tell-tale sign of pressing; 1935-37 issues were made of coarser, heavier paper and flatness is a real give-away. It is hardest to detect in modern issues where they use thinner papers and different printing techniques.
Collectors who do not know anything about pressing are getting defrauded daily and sometimes bigtime.What does one say to an excited collector showing you his newly acquire UNC 1935 $20 for which you know he paid catalogue + and it is clearly a pressed EF with the horirzontal fold line evident ?? For sure, you hope he does not offer to sell it to you in the future !!
I buy and sell pressed notes steadily and am effortful but imperfect in noting that when they are offered for sale. I tell my customers to educate themselves againt honest error and intentional misgrading. Learn or lose.
Waynes Traves has crafted an excellent single page on pressed notes that is very, very informative. Maybe that should be posted. I suggested he send it in to CCN for publishing.
Rick mentioned UNC-60 pressed or UNC-63 pressed. I have been given permission to post for common some draft definitions of UNC-60,63 and 65 which I hope to get I to in a few days. My suggestion on pressed is that it cannot exceed UNC-60. There are a LOT of nice, original UNC notes with the normal counting creases that have been unwisely pressed to look better ( NOT !! ) and these are still UNC-60 I would suggest, but cannot go to UNC-63 after pressing.
Ole Don