The phrase "assiduously kept" is correct and usable in written English.
It can be used to describe something that has been maintained or preserved with great care and attention over time.
Example: "The historical documents were assiduously kept in a climate-controlled archive to ensure their longevity."
Alternatives: "diligently maintained" or "meticulously preserved".
I had all along the line assiduously kept my name from the project.
The published diaries that Tony Benn so assiduously kept across his long political career tell it all.
They took to the streets and clubs in Prada clothes the likes of which the New York fashion critics are assiduously kept unaware.
Currie has assiduously kept a diary since 1987, the dog days of the affair and the references to Major, originally only known as 'B', are legion.
There are more than 200 paintings, 178 sculptures, textiles, ceramics and around 8,000 of the drawings that Miró assiduously kept, going back to when he was an eight-year-old.
During the late 1960s and early 1970s, the years he most assiduously kept a diary, the actor Richard Burton (1925-84) had the following pet names for his wife, Elizabeth Taylor: Lumpy, Booby, Old Fatty, Shumdit, Cantank, Old Snapshot and the Baby.
They both assiduously keep a low profile and refuse to answer any questions about their religion, family members or personal lives.
Many of the afflicted are children whose parents do the shopping and assiduously keep any allergy-inducing products away from the whole family.
The Binc's clientele look like they've stepped from a J. Crew catalogue, and no one raises her voice above a coy murmur, while the bartenders, stirring assiduously, keep to a formal, timeless dress code: white shirts, neckties, black aprons.
Hugo Moreno says there five things to learn from the animal kingdom, including, "Culture can determine corporate survival": "Beehives are known to exhibit a sort of collective superpersonality: Scientists scored 25 hives on such traits as how actively the bees foraged for food, how assiduously they kept up with hive maintenance and how fiercely they defended the hive.
The government had worked assiduously to keep the protests from even happening.
