@nyshadhr9 pointed out today that this doesn't work as expected:
<html>
</head>
<style>
@font-face {
font-family: 'Sample VF';
font-weight: 400;
font-style: normal;
src: url("VfItalSlnt-Regular.ttf") format('truetype');
}
@font-face {
font-family: 'Sample VF';
font-weight: 400;
font-style: italic;
src: url("VfItalSlnt-Regular.ttf") format('truetype');
}
p1 {
font-family: 'Sample VF', display;
font-style: normal;
}
p2 {
font-family: 'Sample VF', display;
font-style: italic;
}
</style>
</head>
<body>
<p1>hello world</p1><br>
<p2>hello world</p2>
</body>
</html>

VfItalSlnt-Regular.zip
Perhaps rather than duplicating the @font-face, this should be possible:
@font-face {
font-family: 'Sample VF';
font-weight: 400;
font-style: normal italic;
src: url("VfItalSlnt-Regular.ttf") format('truetype');
}