You can use PCRE \K operator:
\d{6,10}\K[DC]
It will omit everything in the match up to D or C. You may further tweak this regex allowing or disallowing more characters to the character class [DC].
Have a look at the example.
Sample code:
$re = "/\\d{6,10}\\K[DC]/";
$str = "1309270927C1642,61N654NONREF";
preg_match_all($re, $str, $matches);
Also, here is some more information on \K operator:
The \K "keep out" verb, which is available in Perl, PCRE (C, PHP, R…)
and Ruby 2+. \K tells the engine to drop whatever it has matched so
far from the match to be returned.
Instead of (?<=\b\d+_)[A-Z]+, you can therefore use \b\d+_\K[A-Z]+
The limitations of \K:
Compared with lookbehinds, both the \K and capture group workarounds have limitations:
✽ When you look for multiple matches in a string, at the starting
position of each match attempt, a lookbehind can inspect the
characters behind the current position in the string. Therefore,
against 123, the pattern (?<=\d)\d (match a digit preceded by a digit)
will match both 2 and 3. In contrast, \d\K\d can only match 2, as the
starting position after the first match is immediately before the 3,
and there are not enough digits left for a second match. Likewise,
\d(\d) can only capture 2.
✽ With lookbehinds, you can impose multiple conditions (similar to our
password validation technique) by using multiple lookbehinds. For
instance, to match a digit that is preceded by a lower-case Greek
letter, you can use (?<=\p{Ll})(?<=\p{Greek})\d. The first lookbehind
(?<=\p{Ll}) ensures that the character immediately to the left is a
lower-case letter, and the second lookbehind (?<=\p{Greek}) ensures
that the character immediately to the left belongs to the Greek
script. With the workarounds, you could use \p{Greek}\K\d to match a
digit preceded by a character in the Greek script (or \p{Greek}(\d) to
capture it), but you cannot impose a second condition. To get over
this limitation, you could capture the Greek character and use a
second regex to check that it is a lower-case letter.
Output:
C
