Bug in Handling Archive SEO Title

[abutlwer]

• I've read and understood the contribution guidelines.
• I've searched for any related issues and avoided creating a duplicate issue.
• Originally I posted on the WordPress support forum (Post Link: https://wordpress.org/support/topic/yearly-date-archives-being-mishandled/#post-18061645) but Maybellyne suggested the it was more appropriate to post here.

Please give us a description of what happened

To Reproduce

Step-by-step reproduction instructions

1. Switch on error logging in WordPress config.php file
2. Switch on Yoast SEO Date archives (Yoast SEO > Settings > Advanced > Date archives > Enable Date Archives)
3. Execute a suitable URI to access monthly archives such as /?m=202409
4. Execute a suitable URI to access yearly archives such as /?m=2024

Expected results

1. For Step 3 above: a list of posts with a page heading of Month: October 2024 and an SEO Title in the browser tab of October 2024 Archives .
2. For Step 4 above: a list of posts with a page heading of Year: 2024 and an SEO Title in the browser tab of Year 2024 Archives .

Actual results

1. For Step 3 above: exactly as expected.
2. For Step 4 above: page exactly as expected, but SEO Title in browser tab is 0 . . In addition, several error logging messages reported of the type: PHP Warning: Undefined array key "00" in .../wp-includes/class-wp-locale.php on line 321.

Screenshots, screen recording, code snippet

I think the description above is sufficient.

Technical info

• All software and plugins updated to latest issues.

• If relevant, which editor is affected (or editors):

• Block Editor
• Gutenberg Editor
• Elementor Editor
• Classic Editor
• Other:

• Which browser is affected (or browsers):

• Chrome
• Firefox
• Safari
• Other:

Used versions

• Device you are using: Dell Inspiron Laptop
• Operating system: Windows 10 Home - Linux/Apache web server at Fasthosts for website (cucrc.org)
• PHP version: 8.2.24
• WordPress version: 6.6.2
• WordPress Theme: Twenty Sixteen 3.3
• Yoast SEO version: 23.6
• Gutenberg plugin version:
• Elementor plugin version:
• Classic Editor plugin version:
• Relevant plugins in case of a bug:
  The code seems to be working OK apart from the section that handles the SEO Title. It seems to be failing to check for absent month number, which gets set to zero and so causes problems. However, the page heading section runs correctly and identifies the archive request as being for a year - and the page fill also returns posts for the year.