Why So Many Copies Of Invoice.tpl?

There seems to be multiple copies of invoice.tpl, can someone explain the use of each one i.e.

httpdocs/var/themes_repository/basic/mail/templates/orders/invoice.tpl
httpdocs/design/themes/basic/mail/templates/orders/invoice.tpl
httpdocs/design/backend/mail/templates/orders/invoice.tpl
httpdocs/design/backend/mail/templates/addons/suppliers/invoice.tpl

Are they all the same file, so I can update one and copy it around or are they all different?

Which one's control the PDF printing and which ones are emailed?

httpdocs/var/themes_repository/basic/mail/templates/orders/invoice.tpl - template will be used if you re-install the theme

httpdocs/design/themes/basic/mail/templates/orders/invoice.tpl - template which is used for customer e-mails

httpdocs/design/backend/mail/templates/orders/invoice.tpl - template which is used for admin e-mails

httpdocs/design/backend/mail/templates/addons/suppliers/invoice.tpl - template which is used for supplier e-mails

Unfortunately there is no ability to change only one file and apply changes to rest ones