words - Why use 数年 in あれから１０数年?

My question is on 「あれから１０数年」. My understanding is that this translates to roughly, "It's been 10 years since then."

The dictionary says「数年」 means "several years" or "a number of years". How does the meaning differ from「あれから１０年後」, and why would you use 「数年」when using a specific number?

Answer

あれから１０数年

It means 10 plus several years passed. like 14 to 17 years. 10 to 19 years passed. (corrected)

あれから１０年後

It means exactly 10 years later.

すう‐ねん【数年】

2、3か5、6ぐらいの年数。

source: デジタル大辞泉

じゅう‐すう〔ジフ‐〕【十数】

［語素］単位を表す語の上に付いたり、助数詞を伴ったりして、それが10以上20未満であることを表す。「―メートル」「―人」

source: デジタル大辞泉