Well, we are now certainly stepping into the quagmire of what is the correct vocabulary for naming these series. If we are to call the initial series of 1 to 99,9999 as such "Initial Series" and then the following series イ - 0 to イ - 99,9999 as the "1st Series" it really does not sound right as the distinction between the two (Initial vs. 1st) is not clear at all for the general reader to understand.
I believe the collector developed system of calling イ as the 1st series, ロ the 2nd, ハ the 3rd and so forth in itself was a mistake, because it precludes the initial series as part of the series of serial numbering and have to come up with an even weird name such as "No Series".
Think about it, "no series"..... now what in heck is that supposed to mean ?
I think the best way to describe it is the "Initial Series", "I series", "RO Series", "HA Series" so on and so forth. That being the most closest to the original intent by the Japanese aresenal HQ. But that requires the general reader to understand the Iroha order which ain't happenin', so second best is the way that 03man described, as the "Initial production series", "Second production series (イ)", "Third production series (ロ)", "Fourth production series (ハ)" so on and so forth.