Date code in components marking
The Matsuo date code is explained in more detail in their other datasheets,
such as
p. 2 of the
Matsuo Tantalum Solid Electrolytic Capacitors datasheet.

The codes repeat every 4 years:

The 12 uppercase letters A through M (minus "I") represent the 12 months Jan through December for one of the years 1997, 2001, 2005, 2009, 2013, 2017, ...

The 12 uppercase letters N through Z (minus "O") represent the 12 months Jan through December for one of the years 1998, 2002, 2006, 2010, 2014, 2018, ...

The 12 lowercase letters a through m (minus "i") represent the 12 months Jan through December for one of the years 1999, 2003, 2007, 2011, 2015, 2019, ...

The 12 lowercase letters n through z (minus "o") represent the 12 months Jan through December for one of the years 2000, 2004, 2008, 2012, 2016, 2020, ...

The capacitor you have with date code "M" was apparently manufactured in December in one of the years 1997, 2001, 2005, 2009, or 2013.
(Since you had it in your hands June 2016 we can rule out any later years).

The Jaro date code looks like it might be exactly the same as the Matsuo date code.