MFY Tungsol 6550 tube old versions

In my ARC REF 3 I 'm using a Tungsol 6550 tube with the following code written on the metal base 322NU 3 , it is a smooth grey plate , without holes in the plate .I know 322 is the factorycode of Tungsol and normally the 322 is followed by eq 63=year 45=week 3= shift ?.But I have seen also 322HN-3 and RM-3 .Is there any list of these codes ?
Any help would be wonderfull
Are you sure it's a smooth grey plate? Those letter codes in place of the year code indicate that it's a late vintage black plate circa 1959/1960 just before they went to the smooth grey plates. It might be the first grey plate version. Who knows? I have a number of black plates with those letter codes myself.
I know what you're talking about as I have both the numeric and alphanumeric tube codes on vintage Tung-Sol tubes but I've never seen a list to break down the year and week of production.

I'd be interested myself if anyone is aware of such a list.
Have you tried contacting Brent Jessee or Jim McShane? Those are to NOS tube experts. They should be able to help you.
Oddlots - I had some smooth grey plates with letters in place of the year. I got them from Brent Jessee but traded them a while back.
At first thank you Jedinite24 for JimMcShane 's address ,I sent him an Email , even to tubemuseum and newsensor , just have to wait , and yes Oddlots , I 'm sure it is a smooth grey plate without holes , and looking at the foto 's and description of Tubeworld it could be from 1960 to 1963 , but still want to know the meaning of the code
If you do get a cross reference list could you please share it.
I'll email Brent Jesse about this as well and let you know.
Up until now NO info about the code 's , so we have to look at the tube itself and with the help of the info supplied by TUBEWORLD we can see :
Black plates,1-2-3 getters 1950-1960
Smooth gray plates,all without holes 1960-1963
Gray plates with holes 1963-1970
If supplied with the 322 63=year 45=week 3=shift you have a refference .
Just as a point of information, Tung-Sol (the company that invented the 6550), introduced the first version of the 6550 in 1955 with the single getter black plate.