Programmatically loop form building and only getting the last loop of data in the submit handler (key names, nesting, fieldset wrapping)

Question

I am looping around users with certain conditions so that I can dynamically build a form, this has required a few levels of looping.

1) This is inside a loop, it creates a wrapper fieldset for each user being supplied on each iteration ($uids['userCount'] is a counter)

$form['userToConfirm_' . $uids['userCount']] = array(
    '#title' => t($subsForDisplay[0]['mail']),
    '#type' => 'fieldset',
);
    .....

2) Within that, I loop to contain all the sets of data about that user

Shown here as a fieldset

foreach ($foobar as $foo) {

    $form['userToConfirm_' . $uids['userCount']]
                            [$foo['subset_name']] = array(
        '#title' => t($foo['subset_name']),
        '#type' => 'fieldset',
    );  
        .....

3) Then within that, I pull out the options for each subset

        $form['userToConfirm_' . $uids['userCount']]
                [$foo['subset_name']]
                    [$foo['subset_name'] . 'status'] = array(
            '#title' => t('foo status'),
            '#type' => 'select',
            '#options' => $array,
        );

Based on the following reading: How to place multiple form elements from a loop

and

https://stackoverflow.com/questions/6456671/drupal-form-api-using-foreach-loops-to-build-forms

I think I'm correct in thinking that it's common to unwittingly override the storage every iteration because the keys are not incrementing, or even changing at all, and therefore be left with the last set of data during the form submit.

What I am confused by is why this would be happening when I have already set incrementing key names (for the fieldsets) in my associative array?

Do I need to remove the multi-dimensional part of the $form array, instead of kinda nesting it inside the fieldset? Instead just going straight for every $form key having a unique name?