While deleting all files beginning with the letter a there was still the file Access.txt left. Assuming that it had the correct ownership, why was it not deleted?

File extensions carry no special meaning to the Linux kernel or to rm - a file named 'Access.txt' is treated identically to one named 'Access' with respect to deletion.

The -R flag enables recursive deletion of directory trees and their contents; it has no effect on glob pattern matching for ordinary files in the current directory.

On Linux, rm unlinks the directory entry immediately regardless of whether the file is held open by a process - an open file descriptor keeps the inode alive until closed, but rm does not fail or skip the file.

Hidden files in Linux are denoted by a leading dot in the filename (e.g., '.hidden'); 'Access.txt' starts with an uppercase letter, not a dot, so it is not hidden.

The Linux VFS layer and common filesystems such as ext4 and xfs are case-sensitive by design, meaning 'a' and 'A' are entirely different characters in a filename. A command like 'rm a*' expands the glob to filenames starting with lowercase 'a' only, leaving 'Access.txt' completely untouched because its first character 'A' does not satisfy the pattern.