Kiel diagram showing the positions of our H-rich central stars as purple filled circles. The gray open squares indicate previously analyzed H-rich CSPNe (Herrero et al. 1990; Liebert et al. 1995; McCarthy et al. 1997; Mendez et al. 1988, 1992; Rauch et al. 1999; De Marco et al. 2015; Aller et al. 2015; Reindl et al. 2014, 2017, 2021, 2023; Hillwig et al. 2017; Werner et al. 2019; Jeffery et al. 2023; Bond et al. 2024). The blue solid lines are post-AGB evolutionary tracks from Miller Bertolami (2016), and the light-blue dashed lines are post-RGB evolutionary tracks from Hall et al. (2013). The red dashed-dotted lines correspond to the He-burning main-sequence as well as the zero-age and terminal-age extended horizontal branches. The green dashed line indicates where the He abundances should have decreased down to log(He/H) = −3 according to predictions of Unglaub & Bues (2000).