My answer:
Wa inanaa lafii shakkin is in Hud
Wa inaa lafii shakkin is in Ibrahim
Mimmaa tadcoonaa is in Ibrahim
and in Fussilat (Wa qaaluu quluubunaa fii akinnatin mimmaa tadcoonaa ilayhi)
Mimmaa tadcoonanaa is in Hud in one of the ayahs about the story of Salih AS
When you read wa innanaa know that mimmaa tadconanaa (with two noons) is not in the ayah and vice versa. That is how I remember
I know you mean tadcoonaa where I highlighted as you explained later in your last sentence.
Yeah, that is also how I remember it. But how do you know which comes first? I have a rule that applies to a lot of verses that are hard to differ, and that rule is "the shortest word comes first". To take an example:
The second example in my post was "Wash had bi annaa muslimoon" and "Wash had bi annanaa msulimoon". The first of the two is the shortest as it only has one noon, therefore it is the one that comes first (in Surah Aal Cimraan, the second is in Suurah Al-Maa'idah).
Another example is "Fa man
tabica hudaaya" and "Fa man
ittabaca hudaaya", the first one is shorter as the difference, the highlighted part, consists of three arabic letters while the second consists of five (a letter that is mushaddad consists in reality of two; one saakin and one maftoo7 in this example). Therefore the shorter one comes first (in Suurah Al-Baqarah) while the longer comes later (Suurah Taha). There are more instances like "Qaaladh hab..." and "Qaala fadh hab.." that follow the same pattern.
Obviously this doesn't apply to all look-alike verses, but just a rule that after a while I came to know which verses to use it on and which verses need other rules etc.
Interestingly enough this rule does
not apply to "Wa innaa" and "Wa innanaa" that we were discussing!