SIT vs. no-SIT on air tables

[Mahhz]

If doing three repetitive dives of the same duration and depth, why is a diver penalized for taking a surface interval within the first time bracket versus no surface interval at all (less than 10 minutes)?
Here’s a few examples using NOAA’s new no-deco air table (the old tables are actually even more pronounced).

3 dives at 53’ for 15 min each:
0 min SIT = H
30 min SIT = I

3 dives at 90’ for 10 min each:
0 min SIT = I
30 min SIT = L (14 min deco)

3 dives at 40’ for 47 min each:
0 min SIT = N
30 min SIT = Off the charts

 

[Duke Dive Medicine]

It's because the RGDs are given for a range of bottom times. Using your first example, the first 53'/:15 dive puts you in an RGD of "C", but at 55 feet, a bottom time anywhere from 15 to 19 minutes will put you in the same RGD. The repet table, by necessity, assumes that because you're a "C" diver, your bottom time was 19 minutes vs. 15. If you do the same exercise using a 19 minute bottom time, you come out a "J" diver if you string them all together for 57 minutes, but an "I" diver if you use a 30 minute surface interval between the dives.

 

[Couv]

When I attended commercial diving school in the mid 70ies, we used a rule allowed by the US Tables called the RNT Exception. Basically, if the repetitive dive was to the same depth (or greater) as (than) the previous dive, you were allowed to use the bottom time of the previous dive as the penalty time. Does the RNT Exception still exist in the US Navy tables?