I have notice there are some usage of "im vergangen Jahr", a list of examples can be found here. But I think grammatically it should be "im vergangenen Jahr" (which is also written often). My question is that, is that a general mistake or a purposeful simplification of the adjective ending, when the end is -en
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One of the examples is the following sentence from a document of European Parliament:
Leider ist im vergangen Jahr die Zahl der Menschen, denen wir helfen konnten in ihre Heimat zurückzukehren, stark zurückgegangen, insbesondere aufgrund der Situation in Afghanistan im Südsudan und in der Demokratischen Republik Kongo.