Sorry for asking such a stupid question, I just couldn’t find a trustworthy source on the subject.

In the manga, volume 4, they say Israfel is the 7th Angel right after the fight, except one volume later Fuyutsuki declares Sahaquiel was the 7th with 5 remaining… Im sure it’s just one mistake made by Sadamoto, I just wanted to make sure. Thank you!

Hmm, I don't exactly recall the bits you are referencing but it's important to know that there is a difference between what the public knows and what Seele/Nerv knows, including how many angels there are (because most don't know of the existence of Lilith, believing it to be Adam instead).
So someone from the UN mentioning the number of an Angels is likely to be incorrect.

Afaik, in NGE, the people at the radar surveillance thingy misnumber Matarael because of this reason. And it's been a while since I read the manga, but it seems to be doubling down on Lilith being a secret, and thus more of these numbering inconsistencies can be found.

So it's not a production mistake, it's deliberate.
(or it was a mistake they rectified with an excuse)

The order of the Angels in the manga is discussed in a post-script right after Volume 4. It reads this:

"Recent remarks by Gendo and Fuyutsuki of NERV intriguingly seem to confirm that certain details of the Angels differ in this version of events. Although the first Angel to appear, Sachiel [in Stages 1-5], had been previously assumed to be the Third Angel as so coded in the anime, it is now suggested that in this version of events it was actually the Second. Fuyutsuki commented that the Angel Sahaquiel [Stage 30]—the Tenth Angel as coded in the anime—was actually "[number] seven," to which Gendo replied, "Yes. And five remain." According to this differing classification, then, the Third Angel would be Shamshel [Stages 9-10], the Fourth, Ramiel [Stages 15-19], the Fifth, Gaghiel [Stage 20], and the Sixth, Israfel [Stage 22-26]. Note that the Angels Sandalphon and Matarael—the Eighth and Ninth respectively—have not appeared in this version of events, as they did in the anime, where they followed Israfel and preceded Sahaquiel."

I'm unsure where its mentioned Israfel is the Seventh Angel, though. One thing I'm confident about is that Lilith is NOT considered an Angel in the manga. In Volume 12, when Misato explains her findings about the truth of everything to Shinji, she says this:

"Adam gave birth to twelve Angels, including himself. Likewise, Lilith gave birth to one Angel. Shinji... we humans... are that thirteenth angel, and we never meant to be on this planet."

The wording implies Lilith isn't an Angel, but the Lilin are. This means the Angel order actually goes:

1. Adam
2. Sachiel
3. Samshel
4. Ramiel
5. Gaghiel
6. Israfel
7. Sahaquiel
8. Bardiel
9. Zeruel
10. Arael
11. Armisael
12. Tabris (Kaworu)
13. Lilin (Humans)

This matches both Sahaquiel being described as the Seventh, and Kaworu being described as the Twelfth. I noticed the Wiki actually gets this wrong, but I'm not one to complain, especially since people hardly discuss the manga.

I hope this could help you some way! Sorry for being almost a year late, haha.