What does NVL stand for

It is possible to get completely "invalid" numbers into the database, even using PL/SQL. Your guess about 193 is correct, DUMP(X, 1010)

X = DUMP... -1 = 62,100,102 0 = 128 +1 = 193,2 +2 = 193,3

My guess is the insertion/update code is using a native programming language type e.g. integer, where as it should be using an Oracle NUMBER type. You can't safely assume an Oracle NUMBER is directly equivalent to C# integer. Yes I've seen that odd behaviour before SUM/MAX and other numeric functions were not working properly.

Can you identify the code where those 'bad' numbers came from? The data those bad numbers represented can never be reconstructed, the best you can hope for is to prevent it from happening again.

This looks like a live bug in pg_trgm to me. I can strip away much of the stuff and still reproduce it with this simple test case:

create table foobar (x text);
insert into foobar values ('eldrazi scion'),('eldrazi scio');
create extension pg_trgm ;
create index  on foobar using gin (x gin_trgm_ops);
select * from foobar where x  ~ 'eldrazi (?!scion)';  -- returns 1 row
set enable_seqscan TO off;
select * from foobar where x  ~ 'eldrazi (?!scion)'; -- returns 0 rows

Note that a similar bug was fixed recently (in yet-to-be-released code, commit 16500d2278ab3dd), but that fix does not fix this bug.

I've reported this bug myself, as bug #14623.

And it has now been fixed. When 9.6.3 is released, it should contain the bug-fix.