Monarch was originally owned by Nate Rothstein and Nate DuRoff and the plant was located at 4852 W Jefferson Blvd, Los Angeles, CA. In April 63, Jerry Blaine's Cosnat Dist. Co. bought out Monarch, keeping both Nates on board. (See Billboard 3 April 61 below).
Each disc had ∆ and the matrix number scratched into the wax whilst the label showed the matrix number for the record label, so you would rarely find the Delta matrix on the label, if at all. (Sadly, companies like Alco also used the ∆ sign which confuses the issue more than somewhat). Most Delta presses were "styrene" discs.
The main guide to Delta Pressings was done by Warren Cook for "Record Exchanger" (1972) which was based on the fact that Dot Records used the month and year printed on the label. (So any entry with no record info is probably a Dot pressing.) Any other dates have been supplied by Pascal Perrault and are approximate.
Early in the 60's, Delta stopped using consecutive numbers for the matrix info and began using the same number with an "x" for (probably) the A side.
Some have suggested that if there is a release with a gap between the Delta numbers, then they may have been issued as a 78rpm format as well or a 45rpm format (if the release listed is a 78rpm pressing.)
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Malcolm Chapman and Pascal Perrault
|3 Apr 61|
|5 Jun 61|
|19 Jan 63|
|23 Oct 54|
|24 Aug 63|
|24 Jun 57|