A test pressing is basically a first run copy of a record to be sure everything is correct before making the final run. A test pressing run is very small, and therefore test pressings are very hard to find and quite valuable.

For Genesis, test pressings can be found from many countries in both 7" and 12" form. In the US, the test pressings seem to have come from Presswell until 1977 and then Specialty from 1978 on. In the UK, the test pressings were one-sided only with completely blank labels or no label at all (for the earlier ones).

I will try to find out more information on these, but here is what I was able to determine:

ST -A- 743259- E

ST - I am not totally sure, but I think it means Stereo
A - I have no idea. It may be the batch or run. In the examples below, it is either A or C.
74 - Year of pressing
3259 - Press number. You will notice in the examples below that these go sequentially for each side of the LP, and for each subsequent LP, even when the company name changes.
E - Again, I have no idea. In the examples below it is either A, C, or E

If anyone has any additional information, or can add any test pressings, please let me know.
 

	The Lamb Lies Down on Broadway - October 11, 1974 ST-A-743259-E ST-A-743260-E ST-A-743261-E ST-A-743262-E Presswell Records, no typing or writing on the label.
	A Trick of the Tail - 1976 ST-C-763533-E ST-C-763534-E Presswell Records, very similar label to the one above.
	Wind and Wuthering - December 6, 1976 ST-C-763777-C ST-C-763778-C Presswell Records (references Atlantic), with a typed label.
	Seconds Out - 1977 ST 773959-A ST 773960-A Presswell Records typed label with Atlantic. This is the test pressing for the first LP only. I don't know if a test pressing was done for the other LP.
	Seconds Out - 1977 ST 773959/60 ST 773961/62 Specialty Records later pressing of the above
	And Then There Were Three - February 27, 1978 ST-A-784045-C ST-A-784046-C
	Duke - February 15, 1980 ST-C-804449-A ST-C-804450-A Specialty Records printed label with no writing. Somewhere between the previous test pressing and this one, Presswell was bought or the name was changed to Specialty in Olyphant, PA.
	Abacab - 1981   ST-A-814775 ST-A-814776   Specialty Records, same label as Duke. Includes insert and cover with working titles. Writing on cover looks a lot like Phil's, but hard to say for sure.
	Nursery Cryme - 1982 ST-A-825029-A ST-A-825030-A Specialty Records re-release on a printed label similar to the one above. Same city in PA and same phone number, but different address. Some copies include the insert to the right with some incorrect titles.