Reasonably sure, but willing to be corrected. See this section of the Winetricks code (it’s just shellscript):

        # Don't install if already installed
        if test "${WINETRICKS_FORCE}" != 1 && winetricks_is_installed "$1"; then
            echo "$1 already installed, skipping"
            return "${TRUE}"
        fi

Followed by:

winetricks_is_installed()
{
    unset _W_file _W_file_unix
    if test "${installed_exe1}"; then
        _W_file="${installed_exe1}"
    elif test "${installed_file1}"; then
        _W_file="${installed_file1}"
    else
        return "${FALSE}"  # not installed
    fi

    # Test if the verb has been executed before
    if ! grep -qw "$1" "${WINEPREFIX}/winetricks.log" 2>/dev/null; then
        unset _W_file
        return "${FALSE}"  # not installed
    fi

Winetricks determines whether a verb has been installed by writing and reading to a winetricks.log file found in the root directory of the Wineprefix you’re working with. It also tests if the file actually exists too, but let’s just focus on winetricks.log for simplicity.

The first time Winetricks installs the dxvk verb, which takes the latest DXVK release at the time you run it, it writes dxvk to the winetricks.log file. When a new version of DXVK is released, and you run WINEPREFIX=~/.local/share/wineprefixes/whatever winetricks dxvk, it will hit winetricks_is_installed and read ~/.local/share/wineprefixes/whatever/winetricks.log to see if DXVK is already is installed. It will see that dxvk is in the log file and give up.

When I was writing the Visual Novels on GNU/Linux guide, I did a lot of experimentation with Winetricks. I installed dxvk in a Wineprefix a few months ago and haven’t touched it since then. A new version of DXVK was released three weeks ago. When executing the dxvk verb in that Wineprefix again, I get:

Executing w_do_call dxvk
dxvk already installed, skipping

Years ago, Winetricks would write a new verb definition for every new DXVK release. Presumably when it was much less stable. You can see remnants of that with the 100+ verbs for installing particular DXVK versions. Now it just takes the latest stable release. Yay for the maintainers, because that’s a lot less work. As a side effect, Winetricks doesn’t have a way of updating it normally.

Why doesn’t Winetricks have the ability to update verbs? Well, you’re often installing very specific versions of a native DLL to override the builtin Wine component. You don’t want that changing on you randomly. The w_get_github_latest_release function, which extracts the latest release, was created purely for and only used for DXVK. DXVK is the only component that really works like this in Winetricks.

There is an easy way of updating DXVK anyway. Just run Winetricks with --force:

WINEPREFIX=~/.local/share/wineprefixes/whatever winetricks --force dxvk

Now, admittedly, I misspoke about Winetricks “not supporting updating DXVK”. I learned this option exists just now. So you can force-update it with --force, which bypasses winetricks_is_installed and installs the latest version of DXVK. Guide has been updated accordingly; thank you for making me look into this again!